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<html><title>Programming Ruby: The Pragmatic Programmer's Guide</title><head><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><STYLE TYPE="text/css"><!--
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</STYLE><table bgcolor="#a03030" cellpadding="3" border="0" cellspacing="0"><tr><td colspan="3"><table bgcolor="#902020" cellpadding="20"><tr><td><h1 class="header">Programming Ruby</h1><h3 class="subheader">The Pragmatic Programmer's Guide</h3></td></tr></table></td></tr><tr><td width="33%" align="left"><a class="subheader" href="ref_c_object.html">Previous <</a></td><td width="33%" align="center" valign="middle"><a class="subheader" href="builtins.html">Contents ^</a><br></td><td width="33%" align="right"><a class="subheader" href="ref_c_range.html">Next ></a><br></td></tr></table></head><body bgcolor="white">
<!--
Copyright (c) 2001 by Addison Wesley Longman. This
material may be distributed only subject to the terms and
conditions set forth in the Open Publication License, v1.0 or
later (the latest version is presently available at
http://www.opencontent.org/openpub/).
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<table><tr><td height="20"><img src="dot.gif" width="1" height="20"></td></tr></table><table border="0" width="100%" bgcolor="660066" cellpadding="10"><tr><td valign="center"><font color="white" size="7">class Proc</font></td><td><table border="0"><tr><td><font color="white">
Parent:
</font></td><td><font color="white">Object</font></td></tr><tr><td><font color="white">
Version:
</font></td><td><font color="white">
1.6
</font></td></tr></table></td></tr></table><p></p><H3>Index:</H3><a href="#new">new</a> <a href="#_ob_cb"><i>[ ]</i></a> <a href="#arity"><i>arity</i></a> <a href="#call"><i>call</i></a> <p></p><hr>
<P></P>
<code>Proc</code> objects are blocks of code that have been bound to a set
of local variables. Once bound, the code may be called in different
contexts and still access those variables.
<P></P>
<table bgcolor="#fff0f0" cellspacing="0" border="0" cellpadding="3" width="500">
<tr>
<td colspan="3" valign="top"><code>def genTimes(factor)</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code> return Proc.new {|n| n*factor }</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code>end</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code></code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code>times3 = genTimes(3)</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code>times5 = genTimes(5)</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code></code></td>
</tr>
<tr>
<td valign="top"><code>times3.call(12)</code></td>
<td valign="top"></td>
<td valign="top"><code>36</code></td>
</tr>
<tr>
<td valign="top"><code>times5.call(5)</code></td>
<td valign="top"></td>
<td valign="top"><code>25</code></td>
</tr>
<tr>
<td valign="top"><code>times3.call(times5.call(4))</code></td>
<td valign="top"></td>
<td valign="top"><code>60</code></td>
</tr>
</table>
<P></P>
<P></P>
<table border="0" width="100%" cellpadding="10"><tr><td valign="center" colspan="2" bgcolor="990066"><font color="white" size="6">class methods
</font></td></tr><tr><td valign="center" bgcolor="#ff9999"><font size="4"><a name="new"><b>new</b></a></font></td><td bgcolor="#ffaaaa">
Proc.new <i>[</i>{| | block }
<i>]</i>
-> <i>aProc</i>
</td></tr><td></td><td>
<P></P>
Creates a new <code>Proc</code> object, bound to the current context. It
may be called without a block only within a method with an
attached block, in which case that block is converted to the
<code>Proc</code> object.
<P></P>
<table bgcolor="#fff0f0" cellspacing="0" border="0" cellpadding="3" width="500">
<tr>
<td colspan="3" valign="top"><code>def procFrom</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code> Proc.new</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code>end</code></td>
</tr>
<tr>
<td colspan="3" valign="top"><code>aProc = procFrom { "hello" }</code></td>
</tr>
<tr>
<td valign="top"><code>aProc.call</code></td>
<td valign="top"></td>
<td valign="top"><code>"hello"</code></td>
</tr>
</table>
<P></P>
<P></P>
</td></table>
<P></P>
<table border="0" width="100%" cellpadding="10"><tr><td valign="center" colspan="2" bgcolor="990066"><font color="white" size="6">instance methods
</font></td></tr><tr><td valign="center" bgcolor="#ff9999"><font size="4"><a name="_ob_cb"><b>[ ]</b></a></font></td><td bgcolor="#ffaaaa">
<i>prc</i>[ <i>[</i><i>params</i><i>]<sup>*</sup></i> ]
-> <i>anObject</i>
</td></tr><td></td><td>
<P></P>
Synonym for <code>Proc.call</code>.
<P></P>
</td><tr><td valign="center" bgcolor="#ff9999"><font size="4"><a name="arity"><b>arity</b></a></font></td><td bgcolor="#ffaaaa">
<i>prc</i>.arity -> <i>anInteger</i>
</td></tr><td></td><td>
<P></P>
Returns the number of arguments required by the block. If the
block takes no arguments, returns -1. If it takes one argument,
returns -2. Otherwise, returns a positive argument count unless
the last argument is prefixed with *, in which case the argument
count is negated. The number of required arguments is
<i>anInteger</i> for positive values, and
<code>(</code><i>anInteger</i><code>+1).abs</code> otherwise.
<P></P>
<table bgcolor="#fff0f0" cellspacing="0" border="0" cellpadding="3" width="500">
<tr>
<td valign="top"><code>Proc.new {||}.arity</code></td>
<td valign="top"></td>
<td valign="top"><code>0</code></td>
</tr>
<tr>
<td valign="top"><code>Proc.new {|a|}.arity</code></td>
<td valign="top"></td>
<td valign="top"><code>-1</code></td>
</tr>
<tr>
<td valign="top"><code>Proc.new {|a,b|}.arity</code></td>
<td valign="top"></td>
<td valign="top"><code>2</code></td>
</tr>
<tr>
<td valign="top"><code>Proc.new {|a,b,c|}.arity</code></td>
<td valign="top"></td>
<td valign="top"><code>3</code></td>
</tr>
<tr>
<td valign="top"><code>Proc.new {|*a|}.arity</code></td>
<td valign="top"></td>
<td valign="top"><code>-1</code></td>
</tr>
<tr>
<td valign="top"><code>Proc.new {|a,*b|}.arity</code></td>
<td valign="top"></td>
<td valign="top"><code>-2</code></td>
</tr>
</table>
<P></P>
<P></P>
</td><tr><td valign="center" bgcolor="#ff9999"><font size="4"><a name="call"><b>call</b></a></font></td><td bgcolor="#ffaaaa">
<i>prc</i>.call( <i>[</i><i>params</i><i>]<sup>*</sup></i> )
-> <i>anObject</i>
</td></tr><td></td><td>
<P></P>
Invokes the block, setting the block's parameters to the values
in <i>params</i> using the same rules as used by parallel
assignment. Returns the value of the last expression evaluated
in the block.
<P></P>
<table bgcolor="#fff0f0" cellspacing="0" border="0" cellpadding="3" width="500">
<tr>
<td colspan="3" valign="top"><code>aProc = Proc.new {|a, *b| b.collect {|i| i*a }}</code></td>
</tr>
<tr>
<td valign="top"><code>aProc.call(9, 1, 2, 3)</code></td>
<td valign="top"></td>
<td valign="top"><code>[9, 18, 27]</code></td>
</tr>
<tr>
<td valign="top"><code>aProc[9, 1, 2, 3]</code></td>
<td valign="top"></td>
<td valign="top"><code>[9, 18, 27]</code></td>
</tr>
</table>
<P></P>
<P></P>
</td></table>
<P></P>
<p></p><hr><table bgcolor="#a03030" cellpadding="10" border="0" cellspacing="0"><tr><td width="33%" align="left"><a class="subheader" href="ref_c_object.html">Previous <</a></td><td width="33%" align="center" valign="middle"><a class="subheader" href="builtins.html">Contents ^</a><br></td><td width="33%" align="right"><a class="subheader" href="ref_c_range.html">Next ></a><br></td></tr></table><p></p><font size="-1">Extracted from the book "Programming Ruby -
The Pragmatic Programmer's Guide"</font><br><font size="-3">
Copyright
©
2000 Addison Wesley Longman, Inc. Released under the terms of the
<a href="http://www.opencontent.org/openpub/">Open Publication License</a> V1.0.
<br>
This reference is available for
<a href="http://www.pragmaticprogrammer.com/ruby/downloads/book.html">download</a>.
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