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<H1> 13.13.1 The Package Streams</H1>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> The abstract type Root_Stream_Type is the root
type of the class of stream types. The types in this class represent
different kinds of streams. A new stream type is defined by extending
the root type (or some other stream type), overriding the Read and Write
operations, and optionally defining additional primitive subprograms,
according to the requirements of the particular kind of stream. The predefined
stream-oriented attributes like T'Read and T'Write make dispatching calls
on the Read and Write procedures of the Root_Stream_Type. (User-defined
T'Read and T'Write attributes can also make such calls, or can call the
Read and Write attributes of other types.) </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Examples"><TT><A NAME="I4705"></A><A NAME="I4706"></A><A NAME="I4707"></A><B>package</B> Ada.Streams <B>is</B><BR>
<B>pragma</B> Pure(Streams)<A NAME="I4708"></A>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Examples"><TT> <B>type</B> <A NAME="I4709"></A><A NAME="I4710"></A>Root_Stream_Type <B>is</B> <B>abstract tagged limited private</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4/1</FONT></DIV>
<DIV Class="Examples"><TT>{<I><A HREF="defect1.html#8652/0044">8652/0044</A></I>}
<BR>
<B>type</B> <A NAME="I4711"></A><A NAME="I4712"></A>Stream_Element <B>is</B> <B>mod</B> <I>implementation-defined</I>;<BR>
<B>type</B> <A NAME="I4713"></A><A NAME="I4714"></A>Stream_Element_Offset <B>is</B> <B>range</B> <I>implementation-defined</I>;<BR>
<B>subtype</B> <A NAME="I4715"></A>Stream_Element_Count <B>is</B><BR>
Stream_Element_Offset <B>range</B> 0..Stream_Element_Offset'Last;<BR>
<B>type</B> <A NAME="I4716"></A><A NAME="I4717"></A>Stream_Element_Array <B>is</B><BR>
<B>array</B>(Stream_Element_Offset <B>range</B> <>) <B>of</B><U><B> aliased</B></U> Stream_Element;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I4718"></A><A NAME="I4719"></A>Read(<BR>
Stream : <B>in</B> <B>out</B> Root_Stream_Type;<BR>
Item : <B>out</B> Stream_Element_Array;<BR>
Last : <B>out</B> Stream_Element_Offset) <B>is abstract</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Examples"><TT> <B>procedure</B> <A NAME="I4720"></A><A NAME="I4721"></A>Write(<BR>
Stream : <B>in</B> <B>out</B> Root_Stream_Type;<BR>
Item : <B>in</B> Stream_Element_Array) <B>is abstract</B>;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Examples"><TT><B>private</B><BR>
... -- <I>not specified by the language</I><BR>
<B>end</B> Ada.Streams;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> The Read operation transfers Item'Length stream
elements from the specified stream to fill the array Item. The index
of the last stream element transferred is returned in Last. Last is less
than Item'Last only if the end of the stream is reached.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> The Write operation appends Item to the specified
stream.</DIV>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9.1/1</FONT></DIV>
<DIV Class="Normal"> {<I><A HREF="defect1.html#8652/0044">8652/0044</A></I>}
<U>If Stream_Element'Size is not a multiple of System.Storage_Unit, then
the components of Stream_Element_Array need not be aliased.</U> </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9.a.1/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B><U>If the
Stream_Element'Size is less than the size of System.Storage_Unit, then
components of Stream_Element_Array need not be aliased. This is necessary
as the components of type Stream_Element size might not be addressable
on the target architechture.</U> </FONT></DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>30 See <A HREF="AA-A-12-1.html">A.12.1</A>,
``<A HREF="AA-A-12-1.html">The Package Streams.Stream_IO</A>'' for an
example of extending type Root_Stream_Type. </FONT></DIV>
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