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<H1>ets</H1>
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<H3>MODULE</H3>
<DIV CLASS=REFBODY>
ets
</DIV>

<H3>MODULE SUMMARY</H3>
<DIV CLASS=REFBODY>
Built-In Term Storage
</DIV>

<H3>DESCRIPTION</H3>
<DIV CLASS=REFBODY>

<P>This module is an interface to the Erlang built-in term storage
BIFs. These provide the ability to store very large quantities of
data in an Erlang runtime system, and to have constant access
time to the data. (In the case of <CODE>ordered_set</CODE>, see below,
access time is proportional to the logarithm of the number of
objects stored).
<P>Data is organized as a set of dynamic tables, which can store
tuples. Each table is created by a process. When the process
terminates, the table is automatically destroyed. Every table has
access rights set at creation.
<P>Tables are divided into four different types, <CODE>set</CODE>,
<CODE>ordered_set</CODE>, <CODE>bag</CODE> and <CODE>duplicate_bag</CODE>.
A <CODE>set</CODE> or <CODE>ordered_set</CODE> table can only have one object
associated with each key. A <CODE>bag</CODE> or <CODE>duplicate_bag</CODE> can
have many objects associated with each key.
<P>The number of tables stored at one Erlang node is limited.
The current default limit is approximately 1400 tables. The upper
limit can be increased by setting the environment variable
<CODE>ERL_MAX_ETS_TABLES</CODE> before starting the Erlang runtime
system (i.e. with the <CODE>-env</CODE> option to
<CODE>erl</CODE>/<CODE>werl</CODE>). The actual limit may be slightly higher
than the one specified, but never lower.
<P>Note that there is no automatic garbage collection for tables.
Even if there are no references to a table from any process, it
will not automatically be destroyed unless the owner process
terminates. It can be destroyed explicitly by using
<CODE>delete/1</CODE>.
<P>Some implementation details:
<P>
<UL>

<LI>
In the current implementation, every object insert and
        look-up operation results in one copy of the object.
</LI>


<LI>
This module provides very limited support for concurrent
        updates. No locking is available, but the <CODE>safe_fixtable/2</CODE>
        function can be used to guarantee that a sequence of
        <CODE>first/1</CODE> and <CODE>next/2</CODE> calls will traverse the table
        without errors even if another process (or the same process)
        simultaneously deletes or inserts objects in the table.
</LI>


<LI>
<CODE>'$end_of_table'</CODE> should not be used as a key since
        this atom is used to mark the end of the table when using
        <CODE>first</CODE>/<CODE>next</CODE>.
</LI>


</UL>

<P>In general, the functions below will exit with reason
<CODE>badarg</CODE> if any argument is of the wrong format, or if the
table identifier is invalid.
</DIV>
<A NAME="match_spec"><!-- Empty --></A>
<H3>Match Specifications</H3>
<DIV CLASS=REFBODY>

<P>Some of the functions uses a <STRONG>match specification</STRONG>,
match_spec. A brief explanation is given in
<A HREF="#select/2">select/2</A>. For a detailed
description, see the chapter &#34;Match specifications in Erlang&#34; in
<STRONG>ERTS User's Guide</STRONG>.
</DIV>

<H3>DATA TYPES</H3>
<DIV CLASS=REFBODY>

<PRE>
match_spec()
  a match specification, see above

tid()
  a table identifier, as returned by new/2
    
</PRE>

</DIV>

<H3>EXPORTS</H3>

<P><A NAME="all/0"><STRONG><CODE>all() -&#62; [Tab]</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns a list of all tables at the node. Named tables are
         given by their names, unnamed tables are given by their
         table identifiers.
</DIV>

<P><A NAME="delete/1"><STRONG><CODE>delete(Tab) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Deletes the entire table <CODE>Tab</CODE>.
</DIV>

<P><A NAME="delete/2"><STRONG><CODE>delete(Tab, Key) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Deletes all objects with the key <CODE>Key</CODE> from the table
         <CODE>Tab</CODE>.
</DIV>

<P><A NAME="delete_all_objects/1"><STRONG><CODE>delete_all_objects(Tab) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Delete all objects in the ETS table <CODE>Tab</CODE>. The deletion
         is atomic.
</DIV>

<P><A NAME="delete_object/2"><STRONG><CODE>delete_object(Tab,Object) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Object = tuple()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Delete the exact object <CODE>Object</CODE> from the ETS table,
         leaving objects with the same key but other differences
         (useful for type <CODE>bag</CODE>).
</DIV>

<P><A NAME="file2tab/1"><STRONG><CODE>file2tab(Filename) -&#62; {ok,Tab} | {error,Reason}</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Filename = string() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Reason = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Reads a file produced by <CODE>tab2file/2</CODE> and creates the
         corresponding table <CODE>Tab</CODE>.
</DIV>

<P><A NAME="first/1"><STRONG><CODE>first(Tab) -&#62; Key | '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns the first key <CODE>Key</CODE> in the table <CODE>Tab</CODE>.
         If the table is of the <CODE>ordered_set</CODE> type, the first key
         in Erlang term order will be returned. If the table is of any
         other type, the first key according to the table's internal
         order will be returned. If the table is empty,
         <CODE>'$end_of_table'</CODE> will be returned.
<P>Use <CODE>next/2</CODE> to find subsequent keys in the table.
</DIV>

<P><A NAME="fixtable/2"><STRONG><CODE>fixtable(Tab, true|false) -&#62; true | false</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Warning!" SRC="warning.gif"></TD>
    <TD>

<P>The function is retained for backwards compatibility only.
         Use <CODE>safe_fixtable/2</CODE> instead.    </TD>
  </TR>
</TABLE>

<P>Fixes a table for safe traversal. The function is primarily
         used by the Mnesia DBMS to implement functions which allow
         write operations in a table, although the table is in the
         process of being copied to disk or to another node. It does
         not keep track of when and how tables are fixed.
</DIV>

<P><A NAME="foldl/3"><STRONG><CODE>foldl(Function, Acc0, Tab) -&#62; Acc1</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Function = fun(A, AccIn) -&#62; AccOut</CODE></STRONG><BR>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Acc0 = Acc1 = AccIn = AccOut = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P><CODE>Acc0</CODE> is returned if the table is empty.
         This function is similar to <CODE>lists:foldl/3</CODE>. The order in
         which the elements of the table are traversed is unspecified,
         except for tables of type <CODE>ordered_set</CODE>, for which they
         are traversed first to last.

</DIV>

<P><A NAME="foldr/3"><STRONG><CODE>foldr(Function, Acc0, Tab) -&#62; Acc1</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Function = fun(A, AccIn) -&#62; AccOut</CODE></STRONG><BR>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Acc0 = Acc1 = AccIn = AccOut = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P><CODE>Acc0</CODE> is returned if the table is empty.
         This function is similar to <CODE>lists:foldr/3</CODE>. The order in
         which the elements of the table are traversed is unspecified,
         except for tables of type <CODE>ordered_set</CODE>, for which they
         are traversed last to first.

</DIV>

<P><A NAME="from_dets/2"><STRONG><CODE>from_dets(Tab, DetsTab) -&#62; Tab</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>DetsTab = atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Fills an already created ETS table with the objects in the
         already opened Dets table named <CODE>DetsTab</CODE>. The existing
         objects of the ETS table are kept unless overwritten.
</DIV>

<P><A NAME="fun2ms/1"><STRONG><CODE>fun2ms(LiteralFun) -&#62; MatchSpec</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>LiteralFun -- see below</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Pseudo function that by means of a <CODE>parse_transform</CODE>
         translates <CODE>LiteralFun</CODE> typed as parameter in the
         function call to a
         <A HREF="#match_spec">match_spec</A>. With
         &#34;literal&#34; is meant that the fun needs to textually be written
         as the parameter of the function, it cannot be held in a
         variable which in turn is passed to the function).
<P>The parse transform is implemented in the module
         <CODE>ms_transform</CODE> and the source <STRONG>must</STRONG> include the
         file <CODE>ms_transform.hrl</CODE> in <CODE>stdlib</CODE> for this
         pseudo function to work. Failing to include the hrl file in
         the source will result in a runtime error, not a compile
         time ditto. The include file is easiest included by adding
         the line
         <CODE>-include_lib(&#34;stdlib/include/ms_transform.hrl&#34;).</CODE> to
         the source file.
<P>The fun is very restricted, it can take only a single
         parameter (the object to match): a sole variable or a
         tuple. It needs to use the <CODE>is_</CODE>XXX guard tests.
         Language constructs that have no representation
         in a match_spec (like <CODE>if</CODE>, <CODE>case</CODE>, <CODE>receive</CODE>
         etc) are not allowed.
<P>The return value is the resulting match_spec.
<P>Example:
<PRE>
1&#62; <STRONG>ets:fun2ms(fun({M,N}) when N &#62; 3 -&#62; M end).</STRONG>
[{{'$1','$2'},[{'&#62;','$2',3}],['$1']}]
        
</PRE>

<P>Variables from the environment can be imported, so that this
         works:
<PRE>
2&#62; <STRONG>X=3.</STRONG>
3
3&#62; <STRONG>ets:fun2ms(fun({M,N}) when N &#62; X -&#62; M end).</STRONG>
[{{'$1','$2'},[{'&#62;','$2',{const,3}}],['$1']}]
        
</PRE>

<P>The imported variables will be replaced by match_spec
         <CODE>const</CODE> expressions, which is consistent with the
         static scoping for Erlang funs. Local or global function
         calls can not be in the guard or body of the fun however.
         Calls to builtin match_spec functions of course is allowed:
        
<PRE>
4&#62; <STRONG>ets:fun2ms(fun({M,N}) when N &#62; X, is_atomm(M) -&#62; M end).</STRONG>
Error: fun containing local Erlang function calls
('is_atomm' called in guard) cannot be translated into match_spec
{error,transform_error}
5&#62; <STRONG>ets:fun2ms(fun({M,N}) when N &#62; X, is_atom(M) -&#62; M end).</STRONG>
[{{'$1','$2'},[{'&#62;','$2',{const,3}},{is_atom,'$1'}],['$1']}]
        
</PRE>

<P>As can be seen by the example, the function can be called
         from the shell too. The fun needs to be literally in the call
         when used from the shell as well. Other means than the
         parse_transform are used in the shell case, but more or less
the same restrictions apply (the exception being records,
as they are not handled by the shell).
<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Warning!" SRC="warning.gif"></TD>
    <TD>

<P>If the parse_transform is not applied to a module which
         calls this pseudo function, the call will fail in runtime
         (with a <CODE>badarg</CODE>). The module <CODE>ets</CODE> actually
         exports a function with this name, but it should never
         really be called except for when using the function in the
         shell. If the <CODE>parse_transform</CODE> is properly applied by
         including the <CODE>ms_transform.hrl</CODE> header file, compiled
         code will never call the function, but the function call is
         replaced by a literal match_spec.    </TD>
  </TR>
</TABLE>

<P>For more information, see
         <A HREF="ms_transform.html#top">ms_transform(3)</A>.
        
</DIV>

<P><A NAME="i/0"><STRONG><CODE>i() -&#62; void()</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY>

<P>Displays information about all ETS tables on tty.
</DIV>

<P><A NAME="i/1"><STRONG><CODE>i(Tab) -&#62; void()</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Browses the table <CODE>Tab</CODE> on tty.
</DIV>

<P><A NAME="info/1"><STRONG><CODE>info(Tab) -&#62; [{Item, Value}] | undefined</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Item = atom(), see below</CODE></STRONG><BR>
<STRONG><CODE>Value = term(), see below</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns information about the table <CODE>Tab</CODE> as a list of
         <CODE>{Item, Value}</CODE> tuples.
<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Warning!" SRC="warning.gif"></TD>
    <TD>

<P>In Erlang/OTP R10B and earlier releases, this function
         erroneously returned a tuple. This has now been corrected.
             </TD>
  </TR>
</TABLE>

<P>
<UL>

<LI>
         <CODE>Item=memory, Value=int()</CODE><BR>

         The number of words allocated to the table.
         
</LI>


<LI>
         <CODE>Item=owner, Value=pid()</CODE><BR>

         The pid of the owner of the table.
         
</LI>


<LI>
         <CODE>Item=name, Value=atom()</CODE><BR>

         The name of the table.
         
</LI>


<LI>
         <CODE>Item=size, Value=int()</CODE><BR>

         The number of objects inserted in the table.
         
</LI>


<LI>
         <CODE>Item=node, Value=atom()</CODE><BR>

         The node where the table is stored. This field is no longer
         meaningful as tables cannot be accessed from other nodes.
         
</LI>


<LI>
         <CODE>Item=named_table, Value=true|false</CODE><BR>

         Indicates if the table is named or not.
         
</LI>


<LI>
         <CODE>Item=type, Value=set|ordered_set|bag|duplicate_bag</CODE>
         <BR>

         The table type.
         
</LI>


<LI>
         <CODE>Item=keypos, Value=int()</CODE><BR>

         The key position.
         
</LI>


<LI>
         <CODE>Item=protection, Value=public|protected|private</CODE><BR>

         The table access rights.
         
</LI>


</UL>

</DIV>

<P><A NAME="info/2"><STRONG><CODE>info(Tab, Item) -&#62; Value | undefined</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Item, Value - see below</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns the information associated with <CODE>Item</CODE> for
         the table <CODE>Tab</CODE>. In addition to the <CODE>{Item,Value}</CODE>
         pairs defined for <CODE>info/1</CODE>, the following items are
         allowed:
<P>
<UL>

<LI>
         <CODE>Item=fixed, Value=true|false</CODE><BR>

         Indicates if the table is fixed by any process or not.
         
</LI>


<LI>
         <CODE>Item=safe_fixed, Value={FirstFixed,Info}|false
         </CODE><BR>

         If the table has been fixed using <CODE>safe_fixtable/2</CODE>,
         the call returns a tuple where <CODE>FirstFixed</CODE> is the
         time when the table was first fixed by a process, which
         may or may not be one of the processes it is fixed by
         right now.<BR>


         <CODE>Info</CODE> is a possibly empty lists of tuples
         <CODE>{Pid,RefCount}</CODE>, one tuple for every process the
         table is fixed by right now. <CODE>RefCount</CODE> is the value
         of the reference counter, keeping track of how many times
         the table has been fixed by the process.<BR>


         If the table never has been fixed, the call returns
         <CODE>false</CODE>.<BR>

         
</LI>


</UL>

</DIV>

<P><A NAME="init_table/2"><STRONG><CODE>init_table(Name, InitFun) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Name = atom()</CODE></STRONG><BR>
<STRONG><CODE>InitFun = fun(Arg) -&#62; Res</CODE></STRONG><BR>
<STRONG><CODE>Arg = read | close</CODE></STRONG><BR>
<STRONG><CODE>Res = end_of_input | {[object()], InitFun} | term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Replaces the existing objects of the table <CODE>Tab</CODE> with
         objects created by calling the input function <CODE>InitFun</CODE>,
         see below. This function is provided for compatibility with
         the <CODE>dets</CODE> module, it is not more efficient than filling
         a table by using <CODE>ets:insert/2</CODE>.

        
<P>When called with the argument <CODE>read</CODE> the function
         <CODE>InitFun</CODE> is assumed to return <CODE>end_of_input</CODE> when
         there is no more input, or <CODE>{Objects, Fun}</CODE>, where
         <CODE>Objects</CODE> is a list of objects and <CODE>Fun</CODE> is a new
         input function. Any other value Value is returned as an error
         <CODE>{error, {init_fun, Value}}</CODE>. Each input function will be
         called exactly once, and should an error occur, the last
         function is called with the argument <CODE>close</CODE>, the reply
         of which is ignored.
<P>If the type of the table is <CODE>set</CODE> and there is more
         than one object with a given key, one of the objects is
         chosen. This is not necessarily the last object with the given
         key in the sequence of objects returned by the input
         functions. This holds also for duplicated
         objects stored in tables of type <CODE>duplicate_bag</CODE>.
</DIV>

<P><A NAME="insert/2"><STRONG><CODE>insert(Tab, ObjectOrObjects) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>ObjectOrObjects = tuple() | [tuple()]</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Inserts the object or all of the objects in the list
         <CODE>ObjectOrObjects</CODE> into the table <CODE>Tab</CODE>. If there
         already exists an object with the same key as one of the
         objects, and the table is a <CODE>set</CODE> or <CODE>ordered_set</CODE>
         table, the old object will be replaced. If the list contains
         more than one object with the same key and the table is a
         <CODE>set/ordered_set</CODE>, one will be inserted, which one is
         not defined.
</DIV>

<P><A NAME="insert_new/2"><STRONG><CODE>insert_new(Tab, ObjectOrObjects) -&#62; bool()</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>ObjectOrObjects = tuple() | [tuple()]</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function works exactly like <CODE>insert/2</CODE>, with the
         exception that instead of overwriting objects with the same
         key (in the case of <CODE>set</CODE> or <CODE>ordered_set</CODE>) or
         adding more objects with keys already existing in the table
         (in the case of <CODE>bag</CODE> and <CODE>duplicate_bag</CODE>), it
         simply returns <CODE>false</CODE>. If <CODE>ObjectOrObjects</CODE> is a
         list, the function checks <STRONG>every</STRONG> key prior to
         inserting anything. Nothing will be inserted if not
         <STRONG>all</STRONG> keys present in the list are absent from the
         table.
</DIV>

<P><A NAME="is_compiled_ms/1"><STRONG><CODE>is_compiled_ms(Term) -&#62; bool()</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Term = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function is used to check if a term is a valid
         compiled <A HREF="#match_spec">match_spec</A>.
         The compiled match_spec is an opaque datatype which can
         <STRONG>not</STRONG> be sent between Erlang nodes nor be stored on
         disk. Any attempt to create an external representation of a
         compiled match_spec will result in an empty binary
         (<CODE>&#60;&#60;&#62;&#62;</CODE>). As an example, the following
         expression:
<PRE>
ets:is_compiled_ms(ets:match_spec_compile([{'_',[],[true]}])).
        
</PRE>

<P>will yield <CODE>true</CODE>, while the following expressions:
<PRE>
MS = ets:match_spec_compile([{'_',[],[true]}]),
Broken = binary_to_term(term_to_binary(MS)),
ets:is_compiled_ms(Broken).
        
</PRE>

<P>will yield false, as the variable <CODE>Broken</CODE> will contain
         a compiled match_spec that has passed through external
         representation.
<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Note!" SRC="note.gif"></TD>
    <TD>

<P>The fact that compiled match_specs has no external
         representation is for performance reasons. It may be subject
         to change in future releases, while this interface will
         still remain for backward compatibility reasons.    </TD>
  </TR>
</TABLE>

</DIV>

<P><A NAME="last/1"><STRONG><CODE>last(Tab) -&#62; Key | '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns the last key <CODE>Key</CODE> according to Erlang term
         order in the table <CODE>Tab</CODE> of the <CODE>ordered_set</CODE> type.
         If the table is of any other type, the function is synonymous
         to <CODE>first/2</CODE>. If the table is empty,
         <CODE>'$end_of_table'</CODE> is returned.
<P>Use <CODE>prev/2</CODE> to find preceding keys in the table.
</DIV>

<P><A NAME="lookup/2"><STRONG><CODE>lookup(Tab, Key) -&#62; [Object]</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>
<STRONG><CODE>Object = tuple()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns a list of all objects with the key <CODE>Key</CODE> in
         the table <CODE>Tab</CODE>.
<P>If the table is of type <CODE>set</CODE> or <CODE>ordered_set</CODE>,
         the function returns either the empty list or a list with one
         element, as there cannot be more than one object with the same
         key. If the table is of type <CODE>bag</CODE> or
         <CODE>duplicate_bag</CODE>, the function returns a list of
         arbitrary length.
<P>Note that the time order of object insertions is preserved;
         The first object inserted with the given key will be first
         in the resulting list, and so on.
<P>Insert and look-up times in tables of type <CODE>set</CODE>,
         <CODE>bag</CODE> and <CODE>duplicate_bag</CODE> are constant, regardless
         of the size of the table. For the <CODE>ordered_set</CODE>
         data-type, time is proportional to the (binary) logarithm of
         the number of objects.
</DIV>

<P><A NAME="lookup_element/3"><STRONG><CODE>lookup_element(Tab, Key, Pos) -&#62; Elem</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>
<STRONG><CODE>Pos = int()</CODE></STRONG><BR>
<STRONG><CODE>Elem = term() | [term()]</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>If the table <CODE>Tab</CODE> is of type <CODE>set</CODE> or
         <CODE>ordered_set</CODE>, the function returns the <CODE>Pos</CODE>:th
         element of the object with the key <CODE>Key</CODE>.
<P>If the table is of type <CODE>bag</CODE> or <CODE>duplicate_bag</CODE>,
         the functions returns a list with the <CODE>Pos</CODE>:th element of
         every object with the key <CODE>Key</CODE>.
<P>If no object with the key <CODE>Key</CODE> exists, the function
         will exit with reason <CODE>badarg</CODE>.
</DIV>

<P><A NAME="match/2"><STRONG><CODE>match(Tab, Pattern) -&#62; [Match]</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Pattern = tuple()</CODE></STRONG><BR>
<STRONG><CODE>Match = [term()]</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Matches the objects in the table <CODE>Tab</CODE> against the
         pattern <CODE>Pattern</CODE>.
<P>A pattern is a term that may contain:
<P>
<UL>

<LI>
bound parts (Erlang terms),
</LI>


<LI>
<CODE>'_'</CODE> which matches any Erlang term, and
</LI>


<LI>
pattern variables: <CODE>'$N'</CODE> where
         <CODE>N</CODE>=0,1,...
</LI>


</UL>

<P>The function returns a list with one element for each
         matching object, where each element is an ordered list of
         pattern variable bindings. An example:
<PRE>
6&#62; <STRONG>ets:match(T, '$1').</STRONG> % Matches every object in the table
[[{rufsen,dog,7}],[{brunte,horse,5}],[{ludde,dog,5}]]
7&#62; <STRONG>ets:match(T, {'_',dog,'$1'}).</STRONG>
[[7],[5]]
8&#62; <STRONG>ets:match(T, {'_',cow,'$1'}).</STRONG>
[]
        
</PRE>

<P>If the key is specified in the pattern, the match is very
         efficient. If the key is not specified, i.e. if it is a
         variable or an underscore, the entire table must be searched.
         The search time can be substantial if the table is very large.
        
<P>On tables of the <CODE>ordered_set</CODE> type, the result is in
         the same order as in a <CODE>first/next</CODE> traversal.
</DIV>

<P><A NAME="match/3"><STRONG><CODE>match(Tab, Pattern, Limit) -&#62; {[Match],Continuation} |
        '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Pattern = tuple()</CODE></STRONG><BR>
<STRONG><CODE>Match = [term()]</CODE></STRONG><BR>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Works like <CODE>ets:match/2</CODE> but only returns a limited
         (<CODE>Limit</CODE>) number of matching objects. The
         <CODE>Continuation</CODE> term can then be used in subsequent calls
         to <CODE>ets:match/1</CODE> to get the next chunk of matching
         objects. This is a space efficient way to work on objects in a
         table which is still faster than traversing the table object
         by object using <CODE>ets:first/1</CODE> and <CODE>ets:next/1</CODE>.
<P><CODE>'$end_of_table'</CODE> is returned if the table is empty.
</DIV>

<P><A NAME="match/1"><STRONG><CODE>match(Continuation) -&#62; {[Match],Continuation} |
        '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Match = [term()]</CODE></STRONG><BR>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Continues a match started with <CODE>ets:match/3</CODE>. The next
         chunk of the size given in the initial <CODE>ets:match/3</CODE>
         call is returned together with a new <CODE>Continuation</CODE>
         that can be used in subsequent calls to this function.
<P><CODE>'$end_of_table'</CODE> is returned when there are no more
         objects in the table.
</DIV>

<P><A NAME="match_delete/2"><STRONG><CODE>match_delete(Tab, Pattern) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Pattern = tuple()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Deletes all objects which match the pattern <CODE>Pattern</CODE>
         from the table <CODE>Tab</CODE>. See <CODE>match/2</CODE> for a
         description of patterns.
</DIV>

<P><A NAME="match_object/2"><STRONG><CODE>match_object(Tab, Pattern) -&#62; [Object]</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Pattern = Object = tuple()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Matches the objects in the table <CODE>Tab</CODE> against the
         pattern <CODE>Pattern</CODE>. See <CODE>match/2</CODE> for a description
         of patterns. The function returns a list of all objects which
         match the pattern.
<P>If the key is specified in the pattern, the match is very
         efficient. If the key is not specified, i.e. if it is a
         variable or an underscore, the entire table must be searched.
         The search time can be substantial if the table is very large.
        
<P>On tables of the <CODE>ordered_set</CODE> type, the result is in
         the same order as in a <CODE>first/next</CODE> traversal.
</DIV>

<P><A NAME="match_object/3"><STRONG><CODE>match_object(Tab, Pattern, Limit) -&#62; {[Match],Continuation}
        | '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Pattern = tuple()</CODE></STRONG><BR>
<STRONG><CODE>Match = [term()]</CODE></STRONG><BR>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Works like <CODE>ets:match_object/2</CODE> but only returns a
         limited (<CODE>Limit</CODE>) number of matching objects. The
         <CODE>Continuation</CODE> term can then be used in subsequent calls
         to <CODE>ets:match_object/1</CODE> to get the next chunk of matching
         objects. This is a space efficient way to work on objects in a
         table which is still faster than traversing the table object
         by object using <CODE>ets:first/1</CODE> and <CODE>ets:next/1</CODE>.
<P><CODE>'$end_of_table'</CODE> is returned if the table is empty.
</DIV>

<P><A NAME="match_object/1"><STRONG><CODE>match_object(Continuation) -&#62; {[Match],Continuation} |
        '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Match = [term()]</CODE></STRONG><BR>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Continues a match started with <CODE>ets:match_object/3</CODE>.
         The next chunk of the size given in the initial
         <CODE>ets:match_object/3</CODE> call is returned together with a
         new <CODE>Continuation</CODE> that can be used in subsequent calls
         to this function.
<P><CODE>'$end_of_table'</CODE> is returned when there are no more
         objects in the table.
</DIV>

<P><A NAME="match_spec_compile/1"><STRONG><CODE>match_spec_compile(MatchSpec) -&#62; CompiledMatchSpec</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>
<STRONG><CODE>CompiledMatchSpec = comp_match_spec()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function transforms a
         <A HREF="#match_spec">match_spec</A> into an
         internal representation that can be used in subsequent calls
         to <CODE>ets:match_spec_run/2</CODE>. The internal representation is
         opaque and can not be converted to external term format and
         then back again without losing its properties (meaning it can
         not be sent to a process on another node and still remain a
         valid compiled match_spec, nor can it be stored on disk).
         The validity of a compiled match_spec can be checked using
         <CODE>ets:is_compiled_ms/1</CODE>.
<P>If the term <CODE>MatchSpec</CODE> can not be compiled (does not
         represent a valid match_spec), a <CODE>badarg</CODE> fault is
         thrown.
<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Note!" SRC="note.gif"></TD>
    <TD>

<P>This function has limited use in normal code, it is used by
         Dets to perform the <CODE>dets:select</CODE> operations.    </TD>
  </TR>
</TABLE>

</DIV>

<P><A NAME="match_spec_run/2"><STRONG><CODE>match_spec_run(List,CompiledMatchSpec) -&#62; list()</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>List = [ tuple() ]</CODE></STRONG><BR>
<STRONG><CODE>CompiledMatchSpec = comp_match_spec()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function executes the matching specified in a
         compiled <A HREF="#match_spec">match_spec</A> on
         a list of tuples. The <CODE>CompiledMatchSpec</CODE> term should be
         the result of a call to <CODE>ets:match_spec_compile/1</CODE> and
         is hence the internal representation of the match_spec one
         wants to use.
<P>The matching will be executed on each element in <CODE>List</CODE>
         and the function returns a list containing all results. If an
         element in <CODE>List</CODE> does not match, nothing is returned
         for that element. The length of the result list is therefore
         equal or less than the the length of the parameter
         <CODE>List</CODE>. The two calls in the following example will give
         the same result (but certainly not the same execution
         time...):
<PRE>
Table = ets:new...
MatchSpec = ....
% The following call...
ets:match_spec_run(ets:tab2list(Table),
ets:match_spec_compile(MatchSpec)),
% ...will give the same result as the more common (and more efficient)
ets:select(Table,MatchSpec),
        
</PRE>

<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Note!" SRC="note.gif"></TD>
    <TD>

<P>This function has limited use in normal code, it is used by
         Dets to perform the <CODE>dets:select</CODE> operations and by
         Mnesia during transactions.    </TD>
  </TR>
</TABLE>

</DIV>

<P><A NAME="member/2"><STRONG><CODE>member(Tab, Key) -&#62; true | false</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Works like <CODE>lookup/2</CODE>, but does not return the objects.
         The function returns <CODE>true</CODE> if one or more elements in
         the table has the key <CODE>Key</CODE>, <CODE>false</CODE> otherwise.
</DIV>

<P><A NAME="new/2"><STRONG><CODE>new(Name, Options) -&#62; tid()</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Name = atom()</CODE></STRONG><BR>
<STRONG><CODE>Options = [Option]</CODE></STRONG><BR>
<STRONG><CODE>Option = Type | Access | named_table | {keypos,Pos}</CODE></STRONG><BR>
<STRONG><CODE>Type = set | ordered_set | bag | duplicate_bag
        </CODE></STRONG><BR>
<STRONG><CODE>Access = public | protected | private</CODE></STRONG><BR>
<STRONG><CODE>Pos = int()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Creates a new table and returns a table identifier which can
         be used in subsequent operations. The table identifier can be
         sent to other processes so that a table can be shared between
         different processes within a node.
<P>The parameter <CODE>Options</CODE> is a list of atoms which
         specifies table type, access rights, key position and if the
         table is named or not. If one or more options are left out,
         the default values are used. This means that not specifying
         any options (<CODE>[]</CODE>) is the same as specifying
         <CODE>[set,protected,{keypos,1}]</CODE>.
<P>
<UL>

<LI>
<CODE>set</CODE>
         The table is a <CODE>set</CODE> table - one key, one object,
         no order among objects. This is the default table type.
         <BR>

         
</LI>


<LI>
<CODE>ordered_set</CODE>
         The table is a <CODE>ordered_set</CODE> table - one key, one
         object, ordered in Erlang term order, which is the order
         implied by the &#60; and &#62; operators. Tables of this type
         have a somewhat different behavior in some situations
         than tables of the other types.<BR>

         
</LI>


<LI>
<CODE>bag</CODE>
         The table is a <CODE>bag</CODE> table which can have many
         objects, but only one instance of each object, per key.
         <BR>

         
</LI>


<LI>
<CODE>duplicate_bag</CODE>
         The table is a <CODE>duplicate_bag</CODE> table which can have
         many objects, including multiple copies of the same
         object, per key.<BR>

         
</LI>


<LI>
<CODE>public</CODE>
         Any process may read or write to the table.<BR>

         
</LI>


<LI>
<CODE>protected</CODE>
         The owner process can read and write to the table. Other
         processes can only read the table. This is the default
         setting for the access rights.<BR>

         
</LI>


<LI>
<CODE>private</CODE>
         Only the owner process can read or write to the table.<BR>

         
</LI>


<LI>
<CODE>named_table</CODE>
         If this option is present, the name <CODE>Name</CODE> is
         associated with the table identifier. The name can then
         be used instead of the table identifier in subsequent
         operations.<BR>

         
</LI>


<LI>
<CODE>{keypos,Pos}</CODE>
         Specfies which element in the stored tuples should be
         used as key. By default, it is the first element, i.e.
         <CODE>Pos=1</CODE>. However, this is not always appropriate. In
         particular, we do not want the first element to be the
         key if we want to store Erlang records in a table.<BR>

         Note that any tuple stored in the table must have at
         least <CODE>Pos</CODE> number of elements.<BR>

         
</LI>


</UL>

</DIV>

<P><A NAME="next/2"><STRONG><CODE>next(Tab, Key1) -&#62; Key2 | '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key1 = Key2 = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns the next key <CODE>Key2</CODE>, following the key
         <CODE>Key1</CODE> in the table <CODE>Tab</CODE>. If the table is of the
         <CODE>ordered_set</CODE> type, the next key in Erlang term order is
         returned. If the table is of any other type, the next key
         according to the table's internal order is returned. If there
         is no next key, <CODE>'$end_of_table'</CODE> is returned.
<P>Use <CODE>first/1</CODE> to find the first key in the table.
<P>Unless a table of type <CODE>set</CODE>, <CODE>bag</CODE> or
         <CODE>duplicate_bag</CODE> is protected using
         <CODE>safe_fixtable/2</CODE>, see below, a traversal may fail if
         concurrent updates are made to the table. If the table is of
         type <CODE>ordered_set</CODE>, the function returns the next key in
         order, even if the object does no longer exist.
</DIV>

<P><A NAME="prev/2"><STRONG><CODE>prev(Tab, Key1) -&#62; Key2 | '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key1 = Key2 = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns the previous key <CODE>Key2</CODE>, preceding the key
         <CODE>Key1</CODE> according the Erlang term order in the table
         <CODE>Tab</CODE> of the <CODE>ordered_set</CODE> type. If the table is of
         any other type, the function is synonymous to <CODE>next/2</CODE>.
         If there is no previous key, <CODE>'$end_of_table'</CODE> is
         returned.
<P>Use <CODE>last/1</CODE> to find the last key in the table.
</DIV>

<P><A NAME="rename/2"><STRONG><CODE>rename(Tab, Name) -&#62; Name</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = Name = atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Renames the named table <CODE>Tab</CODE> to the new name
         <CODE>Name</CODE>. Afterwards, the old name can not be used to
         access the table. Renaming an unnamed table has no effect.
</DIV>

<P><A NAME="repair_continuation/2"><STRONG><CODE>repair_continuation(Continuation, MatchSpec) -&#62; Continuation
</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function can be used to restore an opaque continuation
         returned by <CODE>ets:select/3</CODE> or <CODE>ets:select/1</CODE> if the
         continuation has passed through external term format (been
         sent between nodes or stored on disk).
<P>The reason for this function is that continuation terms
         contain compiled match_specs and therefore will be
         invalidated if converted to external term format. Given that
         the original match_spec is kept intact, the continuation can
         be restored, meaning it can once again be used in subsequent
         <CODE>ets:select/1</CODE> calls even though it has been stored on
         disk or on another node.
<P>As an example, the following seqence of calls will fail:
<PRE>
T=ets:new(x,[]),
...
{_,C} = ets:select(T,ets:fun2ms(fun({N,_}=A)
when (N rem 10) =:= 0 -&#62;
A
end),10),
Broken = binary_to_term(term_to_binary(C)),
ets:select(Broken).
        
</PRE>

<P>...while the following sequence will work:
<PRE>
T=ets:new(x,[]),
...
MS = ets:fun2ms(fun({N,_}=A)
when (N rem 10) =:= 0 -&#62;
A
end),
{_,C} = ets:select(T,MS,10),
Broken = binary_to_term(term_to_binary(C)),
ets:select(ets:repair_continuation(Broken,MS)).
        
</PRE>

<P>...as the call to <CODE>ets:repair_continuation/2</CODE> will
         reestablish the (deliberately) invalidated continuation
         <CODE>Broken</CODE>.
<P>
<TABLE CELLPADDING=4>
  <TR>
    <TD VALIGN=TOP><IMG ALT="Note!" SRC="note.gif"></TD>
    <TD>

<P>This function is very rarely needed in application code. It
         is used by Mnesia to implement distributed <CODE>select/3</CODE>
         and <CODE>select/1</CODE> sequences. A normal application would
         either use Mnesia or keep the continuation from being
         converted to external format.
<P>The reason for not having an external representation of a
         compiled match_spec is performance. It may be subject to
         change in future releases, while this interface will remain
         for backward compatibility.    </TD>
  </TR>
</TABLE>

</DIV>

<P><A NAME="safe_fixtable/2"><STRONG><CODE>safe_fixtable(Tab, true|false) -&#62; true</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Fixes a table of the <CODE>set</CODE>, <CODE>bag</CODE> or
         <CODE>duplicate_bag</CODE> table type for safe traversal.
<P>A process fixes a table by calling
         <CODE>safe_fixtable(Tab,true)</CODE>. The table remains fixed until
         the process releases it by calling
         <CODE>safe_fixtable(Tab,false)</CODE>, or until the process
         terminates.
<P>If several processes fix a table, the table will remain fixed
         until all processes have released it (or terminated).
         A reference counter is kept on a per process basis, and N
         consecutive fixes requires N releases to actually release
         the table.
<P>When a table is fixed, a sequence of <CODE>first/1</CODE> and
         <CODE>next/2</CODE> calls are guaranteed to succeed even if objects
         are removed during the traversal. An example:
<PRE>
clean_all_with_value(Tab,X) -&#62;
    safe_fixtable(Tab,true),
    clean_all_with_value(Tab,X,ets:first(Tab)),
    safe_fixtable(Tab,false).

clean_all_with_value(Tab,X,'$end_of_table') -&#62;
    true;
clean_all_with_value(Tab,X,Key) -&#62;
    case ets:lookup(Tab,Key) of
        [{Key,X}] -&#62;
            ets:delete(Tab,Key);
        _ -&#62;
            true
    end,
    clean_all_with_value(Tab,X,ets:next(Tab,Key)).
        
</PRE>

<P>Note that no deleted objects are actually removed from a
         fixed table until it has been released. If a process fixes a
         table but never releases it, the memory used by the deleted
         objects will never be freed. The performance of operations on
         the table will also degrade significantly.
<P>Use <CODE>info/2</CODE> to retrieve information about which
         processes have fixed which tables. A system with a lot of
         processes fixing tables may need a monitor which sends alarms
         when tables have been fixed for too long.
<P>Note that for tables of the <CODE>ordered_set</CODE> type,
         <CODE>safe_fixtable/2</CODE> is not necessary as calls to
         <CODE>first/1</CODE> and <CODE>next/2</CODE> will always succeed.
</DIV>

<P><A NAME="select/2"><STRONG><CODE>select(Tab, MatchSpec) -&#62; [Match]</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Match = term()</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Matches the objects in the table <CODE>Tab</CODE> using a
         <A HREF="#match_spec">match_spec</A>. This is a
         more general call than the <CODE>ets:match/2</CODE> and
         <CODE>ets:match_object/2</CODE> calls. In its simplest forms the
         match_specs look like this:
<P>
<UL>

<LI>
MatchSpec = [MatchFunction]
         
</LI>


<LI>
MatchFunction = {MatchHead, [Guard], [Result]}
         
</LI>


<LI>
MatchHead = &#34;Pattern as in ets:match&#34;
         
</LI>


<LI>
Guard = {&#34;Guardtest name&#34;, ...}
         
</LI>


<LI>
Result = &#34;Term construct&#34;
        
</LI>


</UL>

<P>This means that the match_spec is always a list of one or
         more tuples (of arity 3). The tuples first element should be
         a pattern as described in the documentation of
         <CODE>ets:match/2</CODE>. The second element of the tuple should
         be a list of 0 or more guard tests (described below). The
         third element of the tuple should be a list containing a
         description of the value to actually return. In almost all
         normal cases the list contains exactly one term which fully
         describes the value to return for each object.
<P>The return value is constructed using the &#34;match variables&#34;
         bound in the MatchHead or using the special match variables
         <CODE>'$_'</CODE> (the whole matching object) and <CODE>'$$'</CODE> (all
         match variables in a list), so that the following
         <CODE>ets:match/2</CODE> expression:
<PRE>
ets:match(Tab,{'$1','$2','$3'})
        
</PRE>

<P>is exactly equivalent to:
<PRE>
ets:select(Tab,[{{'$1','$2','$3'},[],['$$']}])
        
</PRE>

<P>- and the following <CODE>ets:match_object/2</CODE> call:
<PRE>
ets:match_object(Tab,{'$1','$2','$1'})
        
</PRE>

<P>is exactly equivalent to
<PRE>
ets:select(Tab,[{{'$1','$2','$1'},[],['$_']}])
        
</PRE>

<P>Composite terms can be constructed in the <CODE>Result</CODE> part
         either by simply writing a list, so that this code:
<PRE>
ets:select(Tab,[{{'$1','$2','$3'},[],['$$']}])
        
</PRE>

<P>gives the same output as:
<PRE>
ets:select(Tab,[{{'$1','$2','$3'},[],[['$1','$2','$3']]}])
        
</PRE>

<P>i.e. all the bound variables in the match head as a list. If
         tuples are to be constructed, one has to write a tuple of
         arity 1 with the single element in the tuple being the tuple
         one wants to construct (as an ordinary tuple could be mistaken
         for a <CODE>Guard</CODE>). Therefore the following call:
<PRE>
ets:select(Tab,[{{'$1','$2','$1'},[],['$_']}])
        
</PRE>

<P>gives the same output as:
<PRE>
ets:select(Tab,[{{'$1','$2','$1'},[],[{{'$1','$2','$3'}}]}])
        
</PRE>

<P>- this syntax is equivalent to the syntax used in the trace
         patterns (see
         <A HREF="javascript:erlhref('../../../../', 'runtime_tools', 'dbg.html');">dbg(3)</A>).
<P>The <CODE>Guard</CODE>s are constructed as tuples where the first
         element is the name of the test and the rest of the elements
         are the parameters of the test. To check for a specific type
         (say a list) of the element bound to the match variable
         <CODE>'$1'</CODE>, one would write the test as
         <CODE>{is_list, '$1'}</CODE>. If the test fails, the object in the
         table will not match and the next <CODE>MatchFunction</CODE> (if
         any) will be tried. Most guard tests present in Erlang can be
         used, but only the new versions prefixed <CODE>is_</CODE> are
         allowed (like <CODE>is_float</CODE>, <CODE>is_atom</CODE> etc).
<P>The <CODE>Guard</CODE> section can also contain logic and
         arithmetic operations, which are written with the same syntax
         as the guard tests (prefix notation), so that a guard test
         written in Erlang looking like this:
<PRE>
is_integer(X), is_integer(Y), X + Y &#60; 4711
        
</PRE>

<P>is expressed like this (X replaced with '$1' and Y with
         '$2'):
<PRE>
[{is_integer, '$1'}, {is_integer, '$2'}, {'&#60;', {'+', '$1', '$2'}, 4711}]
        
</PRE>

</DIV>

<P><A NAME="select/3"><STRONG><CODE>select(Tab, MatchSpec, Limit) -&#62; {[Match],Continuation} |
        '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Match = term()</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Works like <CODE>ets:select/2</CODE> but only returns a limited
         (<CODE>Limit</CODE>) number of matching objects. The
         <CODE>Continuation</CODE> term can then be used in subsequent calls
         to <CODE>ets:select/1</CODE> to get the next chunk of matching
         objects. This is a space efficient way to work on objects in a
         table which is still faster than traversing the table object
         by object using <CODE>ets:first/1</CODE> and <CODE>ets:next/1</CODE>.
<P><CODE>'$end_of_table'</CODE> is returned if the table is empty.
</DIV>

<P><A NAME="select/1"><STRONG><CODE>select(Continuation) -&#62; {[Match],Continuation} |
        '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Match = term()</CODE></STRONG><BR>
<STRONG><CODE>Continuation = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Continues a match started with
         <CODE>ets:select/3</CODE>. The next
         chunk of the size given in the initial <CODE>ets:select/3</CODE>
         call is returned together with a new <CODE>Continuation</CODE>
         that can be used in subsequent calls to this function.
<P><CODE>'$end_of_table'</CODE> is returned when there are no more
         objects in the table.
</DIV>

<P><A NAME="select_delete/2"><STRONG><CODE>select_delete(Tab, MatchSpec) -&#62; NumDeleted</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Object = tuple()</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>
<STRONG><CODE>NumDeleted = integer()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Matches the objects in the table <CODE>Tab</CODE> using a
         <A HREF="#match_spec">match_spec</A>. If the
         match_spec returns <CODE>true</CODE> for an object, that object is
         removed from the table. For any other result from the
         match_spec the object is retained. This is a more general
         call than the <CODE>ets:match_delete/2</CODE> call.
<P>The function returns the number of objects actually
         deleted from the table.
</DIV>

<P><A NAME="select_count/2"><STRONG><CODE>select_count(Tab, MatchSpec) -&#62; NumMatched</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Object = tuple()</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>
<STRONG><CODE>NumMatched = integer()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Matches the objects in the table <CODE>Tab</CODE> using a
         <A HREF="#match_spec">match_spec</A>. If the
         match_spec returns <CODE>true</CODE> for an object, that object
         considered a match and is counted. For any other result from
         the match_spec the object is not considered a match and is
         therefore not counted.
<P>The function could be described as a <CODE>match_delete/2</CODE>
         that does not actually delete any elements, but only counts
         them.
<P>The function returns the number of objects matched.
</DIV>

<P><A NAME="slot/2"><STRONG><CODE>slot(Tab, I) -&#62; [Object] | '$end_of_table'</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>I = int()</CODE></STRONG><BR>
<STRONG><CODE>Object = tuple()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function is mostly for debugging purposes, Normally
         one should use <CODE>first/next</CODE> or <CODE>last/prev</CODE> instead.
        
<P>Returns all objects in the <CODE>I</CODE>:th slot of the table
         <CODE>Tab</CODE>. A table can be traversed by repeatedly calling
         the function, starting with the first slot <CODE>I=0</CODE> and
         ending when <CODE>'$end_of_table'</CODE> is returned.
         The function will fail with reason <CODE>badarg</CODE> if the
         <CODE>I</CODE> argument is out of range.
<P>Unless a table of type <CODE>set</CODE>, <CODE>bag</CODE> or
         <CODE>duplicate_bag</CODE> is protected using
         <CODE>safe_fixtable/2</CODE>, see above, a traversal may fail if
         concurrent updates are made to the table. If the table is of
         type <CODE>ordered_set</CODE>, the function returns a list
         containing the <CODE>I</CODE>:th object in Erlang term order.
</DIV>

<P><A NAME="tab2file/2"><STRONG><CODE>tab2file(Tab, Filename) -&#62; ok | {error,Reason}</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Filename = string() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Reason = term()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Dumps the table <CODE>Tab</CODE> to the file <CODE>Filename</CODE>.
         The implementation of this function is not efficient.
</DIV>

<P><A NAME="tab2list/1"><STRONG><CODE>tab2list(Tab) -&#62; [Object]</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Object = tuple()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Returns a list of all objects in the table <CODE>Tab</CODE>.
</DIV>

<P><A NAME="table/2"><STRONG><CODE>table(Tab [, Options]) -&#62; QueryHandle</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>QueryHandle = -a query handle, see qlc(3)-</CODE></STRONG><BR>
<STRONG><CODE>Options = [Option] | Option</CODE></STRONG><BR>
<STRONG><CODE>Option = {n_objects, NObjects}
         | {traverse, TraverseMethod}</CODE></STRONG><BR>
<STRONG><CODE>NObjects = default | integer() &#62; 0</CODE></STRONG><BR>
<STRONG><CODE>TraverseMethod = first_next
         | last_prev
         | select
         | {select, MatchSpec}</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P><A NAME="qlc_table"><!-- Empty --></A>Returns a QLC (Query List
         Comprehension) query handle. The module <CODE>qlc</CODE> implements
         a query language aimed mainly at Mnesia but ETS tables, Dets
         tables, and lists are also recognized by QLC as sources of
         data. Calling <CODE>ets:table/1,2</CODE> is the means to make the
         ETS table <CODE>Tab</CODE> usable to QLC.
<P>When there are only simple restrictions on the key position
         QLC uses <CODE>ets:lookup/2</CODE> to look up the keys, but when
         that is not possible the whole table is traversed. The
         option <CODE>traverse</CODE> determines how this is done:
<P>
<UL>

<LI>
         <CODE>first_next</CODE>. The table is traversed one key at
         a time by calling <CODE>ets:first/1</CODE> and
         <CODE>ets:next/2</CODE>.<BR>

         
</LI>


<LI>
         <CODE>last_prev</CODE>. The table is traversed one key at
         a time by calling <CODE>ets:last/1</CODE> and
         <CODE>ets:prev/2</CODE>.<BR>

         
</LI>


<LI>
         <CODE>select</CODE>. The table is traversed by calling
         <CODE>ets:select/3</CODE> and <CODE>ets:select/1</CODE>. The option
         <CODE>n_objects</CODE> determines the number of objects
         returned (the third argument of <CODE>select/3</CODE>); the
         default is to return <CODE>100</CODE> objects at a time. The
         <A HREF="#match_spec">match_spec</A> (the
         second argument of <CODE>select/3</CODE>) is assembled by QLC:
         simple filters are translated into equivalent match_specs
         while more complicated filters have to be applied to all
         objects returned by <CODE>select/3</CODE> given a match_spec
         that matches all objects.<BR>

         
</LI>


<LI>
         <CODE>{select, MatchSpec}</CODE>. As for <CODE>select</CODE>
         the table is traversed by calling <CODE>ets:select/3</CODE> and
         <CODE>ets:select/1</CODE>. The difference is that the
         match_spec is explicitly given. This is how to state
         match_specs that cannot easily be expressed within the
         syntax provided by QLC.<BR>

         
</LI>


</UL>

<P>The following example uses an explicit match_spec to
         traverse the table:
<PRE>
9&#62; <STRONG>ets:insert(Tab = ets:new(t, []), [{1,a},{2,b},{3,c},{4,d}]),</STRONG>
<STRONG>MS = ets:fun2ms(fun({X,Y}) when (X &#62; 1) or (X &#60; 5) -&#62; {Y} end),</STRONG>
<STRONG>QH1 = ets:table(Tab, [{traverse, {select, MS}}]).</STRONG>
        
</PRE>

<P>An example with implicit match_spec:
<PRE>
10&#62; <STRONG>QH2 = qlc:q([{Y} || {X,Y} &#60;- ets:table(Tab), (X &#62; 1) or (X &#60; 5)]).</STRONG>
        
</PRE>

<P>The latter example is in fact equivalent to the former which
         can be verified using the function <CODE>qlc:info/1</CODE>:
<PRE>
11&#62; <STRONG>qlc:info(QH1) =:= qlc:info(QH2).</STRONG>
true
        
</PRE>

<P><CODE>qlc:info/1</CODE> returns information about a query handle,
         and in this case identical information is returned for the
         two query handles.
</DIV>

<P><A NAME="test_ms/2"><STRONG><CODE>test_ms(Tuple, MatchSpec) -&#62; {ok, Result} | {error, Errors}
</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tuple = tuple()</CODE></STRONG><BR>
<STRONG><CODE>MatchSpec = match_spec()</CODE></STRONG><BR>
<STRONG><CODE>Result = term()</CODE></STRONG><BR>
<STRONG><CODE>Errors = [{warning|error, string()}]
</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function is a utility to test a
         <A HREF="#match_spec">match_spec</A> used in
         calls to <CODE>ets:select/2</CODE>. The function both tests
         <CODE>MatchSpec</CODE> for &#34;syntactic&#34; correctness and runs the
         match_spec against the object <CODE>Tuple</CODE>. If the match_spec
         contains errors, the tuple <CODE>{error, Errors}</CODE> is returned
         where <CODE>Errors</CODE> is a list of natural language
         descriptions of what was wrong with the match_spec. If the
         match_spec is syntactically OK, the function returns
         <CODE>{ok,Term}</CODE> where <CODE>Term</CODE> is what would have been
         the result in a real <CODE>ets:select/2</CODE> call or <CODE>false</CODE>
         if the match_spec does not match the object <CODE>Tuple</CODE>.
<P>This is a useful debugging and test tool, especially when
         writing complicated <CODE>ets:select/2</CODE> calls.
</DIV>

<P><A NAME="to_dets/2"><STRONG><CODE>to_dets(Tab, DetsTab) -&#62; Tab</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>DetsTab = atom()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>Fills an already created/opened Dets table with the objects
         in the already opened ETS table named <CODE>Tab</CODE>. The Dets
         table is emptied before the objects are inserted.
</DIV>

<P><A NAME="update_counter/6"><STRONG><CODE>update_counter(Tab, Key, {Pos,Incr,Threshold,SetValue}) -&#62;
        Result</CODE></STRONG></A><BR>
<A NAME="update_counter/4"><STRONG><CODE>update_counter(Tab, Key, {Pos,Incr}) -&#62; Result</CODE></STRONG></A><BR>
<A NAME="update_counter/3"><STRONG><CODE>update_counter(Tab, Key, Incr) -&#62; Result</CODE></STRONG></A><BR>

<DIV CLASS=REFBODY><P>Types:
  <DIV CLASS=REFTYPES>
<P>
<STRONG><CODE>Tab = tid() | atom()</CODE></STRONG><BR>
<STRONG><CODE>Key = term()</CODE></STRONG><BR>
<STRONG><CODE>Pos = Incr = Threshold = SetValue = Result = int()</CODE></STRONG><BR>

  </DIV>
</DIV>

<DIV CLASS=REFBODY>

<P>This function provides an efficient way to update a counter,
         without the hassle of having to look up an object, update the
         object by incrementing an element and insert the resulting
         object into the table again. (The update is done atomically;
         i.e. no process can access the ets table in the middle of the
         operation.)
<P>It will destructively update the object with key <CODE>Key</CODE>
         in the table <CODE>Tab</CODE> by adding <CODE>Incr</CODE> to the element
         at the <CODE>Pos</CODE>:th position. The new counter value is
         returned. If no position is specified, the element directly
         following the key (<CODE>&#60;keypos&#62;+1</CODE>) is updated.
<P>If a <CODE>Threshold</CODE> is specified, the counter will be
         reset to the value <CODE>SetValue</CODE> if the following
         conditions occur:
<P>
<UL>

<LI>
The <CODE>Incr</CODE> is not negative (<CODE>&#62;= 0</CODE>) and the
         result would be greater than (<CODE>&#62;</CODE>) <CODE>Threshold</CODE>
         
</LI>


<LI>
The <CODE>Incr</CODE> is negative (<CODE>&#60; 0</CODE>) and the
         result would be less than (<CODE>&#60;</CODE>)
         <CODE>Threshold</CODE>
</LI>


</UL>

<P>The function will fail with reason <CODE>badarg</CODE> if:
<P>
<UL>

<LI>
the table is not of type <CODE>set</CODE> or
         <CODE>ordered_set</CODE>,
</LI>


<LI>
no object with the right key exists,
</LI>


<LI>
the object has the wrong arity,
</LI>


<LI>
the element to update is not an integer,
</LI>


<LI>
the element to update is also the key, or,
</LI>


<LI>
any of <CODE>Pos</CODE>, <CODE>Incr</CODE>, <CODE>Threshold</CODE> or
         <CODE>SetValue</CODE> is not an integer
</LI>


</UL>

</DIV>

<H3>AUTHORS</H3>
<DIV CLASS=REFBODY>
Claes Wikstrom, Tony Rogvall, Patrik Nyblom - support@erlang.ericsson.se<BR>

</DIV>
<CENTER>
<HR>
<SMALL>stdlib 1.14.2<BR>
Copyright &copy; 1991-2006
<A HREF="http://www.erlang.se">Ericsson AB</A><BR>
</SMALL>
</CENTER>
</BODY>
</HTML>