watch.html
来自「perl教程」· HTML 代码 · 共 295 行 · 第 1/2 页
HTML
295 行
<?xml version="1.0" ?>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<!-- saved from url=(0017)http://localhost/ -->
<script language="JavaScript" src="../../displayToc.js"></script>
<script language="JavaScript" src="../../tocParas.js"></script>
<script language="JavaScript" src="../../tocTab.js"></script>
<link rel="stylesheet" type="text/css" href="../../scineplex.css">
<title>Tie::Watch - place watchpoints on Perl variables.</title>
<link rel="stylesheet" href="../../Active.css" type="text/css" />
<meta http-equiv="content-type" content="text/html; charset=utf-8" />
<link rev="made" href="mailto:" />
</head>
<body>
<script>writelinks('__top__',2);</script>
<h1><a>Tie::Watch - place watchpoints on Perl variables.</a></h1>
<p><a name="__index__"></a></p>
<!-- INDEX BEGIN -->
<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#methods">METHODS</a></li>
<li><a href="#efficiency_considerations">EFFICIENCY CONSIDERATIONS</a></li>
<li><a href="#author">AUTHOR</a></li>
<li><a href="#history">HISTORY</a></li>
<li><a href="#copyright">COPYRIGHT</a></li>
</ul>
<!-- INDEX END -->
<hr />
<p>
</p>
<h1><a name="name">NAME</a></h1>
<pre>
Tie::Watch - place watchpoints on Perl variables.</pre>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
<span class="keyword">use</span> <span class="variable">Tie::Watch</span><span class="operator">;</span>
</pre>
<pre>
<span class="variable">$watch</span> <span class="operator">=</span> <span class="variable">Tie::Watch</span><span class="operator">-></span><span class="variable">new</span><span class="operator">(</span>
<span class="string">-variable</span> <span class="operator">=></span> <span class="operator">\</span><span class="variable">$frog</span><span class="operator">,</span>
<span class="string">-debug</span> <span class="operator">=></span> <span class="number">1</span><span class="operator">,</span>
<span class="string">-shadow</span> <span class="operator">=></span> <span class="number">0</span><span class="operator">,</span>
<span class="string">-fetch</span> <span class="operator">=></span> <span class="operator">[</span><span class="operator">\&</span><span class="variable">fetch</span><span class="operator">,</span> <span class="string">'arg1'</span><span class="operator">,</span> <span class="string">'arg2'</span><span class="operator">,</span> <span class="operator">...,</span> <span class="string">'argn'</span><span class="operator">]</span><span class="operator">,</span>
<span class="string">-store</span> <span class="operator">=></span> <span class="operator">\&</span><span class="variable">store</span><span class="operator">,</span>
<span class="string">-destroy</span> <span class="operator">=></span> <span class="keyword">sub</span><span class="variable"> </span><span class="operator">{</span><span class="keyword">print</span> <span class="string">"Final value=$frog.\n"</span><span class="operator">},</span>
<span class="operator">}</span>
<span class="variable">%vinfo</span> <span class="operator">=</span> <span class="variable">$watch</span><span class="operator">-></span><span class="variable">Info</span><span class="operator">;</span>
<span class="variable">$args</span> <span class="operator">=</span> <span class="variable">$watch</span><span class="operator">-></span><span class="variable">Args</span><span class="operator">(-</span><span class="variable">fetch</span><span class="operator">);</span>
<span class="variable">$val</span> <span class="operator">=</span> <span class="variable">$watch</span><span class="operator">-></span><span class="variable">Fetch</span><span class="operator">;</span>
<span class="keyword">print</span> <span class="string">"val="</span><span class="operator">,</span> <span class="variable">$watch</span><span class="operator">-></span><span class="variable">Say</span><span class="operator">(</span><span class="variable">$val</span><span class="operator">),</span> <span class="string">".\n"</span><span class="operator">;</span>
<span class="variable">$watch</span><span class="operator">-></span><span class="variable">Store</span><span class="operator">(</span><span class="string">'Hello'</span><span class="operator">);</span>
<span class="variable">$watch</span><span class="operator">-></span><span class="variable">Unwatch</span><span class="operator">;</span>
</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>This class module binds one or more subroutines of your devising to a
Perl variable. All variables can have <strong>FETCH</strong>, <strong>STORE</strong> and
<strong>DESTROY</strong> callbacks. Additionally, arrays can define <strong>CLEAR</strong>, <strong>EXTEND</strong>,
<strong>FETCHSIZE</strong>, <strong>POP</strong>, <strong>PUSH</strong>, <strong>SHIFT</strong>, <strong>SPLICE</strong>, <strong>STORESIZE</strong> and
<strong>UNSHIFT</strong> callbacks, and hashes can define <strong>CLEAR</strong>, <strong>DELETE</strong>, <strong>EXISTS</strong>,
<strong>FIRSTKEY</strong> and <strong>NEXTKEY</strong> callbacks. If these term are unfamiliar to you,
I <em>really</em> suggest you read <a href="../../lib/Pod/perltie.html">the perltie manpage</a>.</p>
<p>With Tie::Watch you can:</p>
<pre>
. alter a variable's value
. prevent a variable's value from being changed
. invoke a Perl/Tk callback when a variable changes
. trace references to a variable</pre>
<p>Callback format is patterned after the Perl/Tk scheme: supply either a
code reference, or, supply an array reference and pass the callback
code reference in the first element of the array, followed by callback
arguments. (See examples in the Synopsis, above.)</p>
<p>Tie::Watch provides default callbacks for any that you fail to
specify. Other than negatively impacting performance, they perform
the standard action that you'd expect, so the variable behaves
"normally". Once you override a default callback, perhaps to insert
debug code like print statements, your callback normally finishes by
calling the underlying (overridden) method. But you don't have to!</p>
<p>To map a tied method name to a default callback name simply lowercase
the tied method name and uppercase its first character. So FETCH
becomes Fetch, NEXTKEY becomes Nextkey, etcetera.</p>
<p>Here are two callbacks for a scalar. The <strong>FETCH</strong> (read) callback does
nothing other than illustrate the fact that it returns the value to
assign the variable. The <strong>STORE</strong> (write) callback uppercases the
variable and returns it. In all cases the callback <em>must</em> return the
correct read or write value - typically, it does this by invoking the
underlying method.</p>
<pre>
<span class="keyword">my</span> <span class="variable">$fetch_scalar</span> <span class="operator">=</span> <span class="keyword">sub</span><span class="variable"> </span><span class="operator">{</span>
<span class="keyword">my</span><span class="operator">(</span><span class="variable">$self</span><span class="operator">)</span> <span class="operator">=</span> <span class="variable">@_</span><span class="operator">;</span>
<span class="variable">$self</span><span class="operator">-></span><span class="variable">Fetch</span><span class="operator">;</span>
<span class="operator">};</span>
</pre>
<pre>
<span class="keyword">my</span> <span class="variable">$store_scalar</span> <span class="operator">=</span> <span class="keyword">sub</span><span class="variable"> </span><span class="operator">{</span>
<span class="keyword">my</span><span class="operator">(</span><span class="variable">$self</span><span class="operator">,</span> <span class="variable">$new_val</span><span class="operator">)</span> <span class="operator">=</span> <span class="variable">@_</span><span class="operator">;</span>
<span class="variable">$self</span><span class="operator">-></span><span class="variable">Store</span><span class="operator">(</span><span class="keyword">uc</span> <span class="variable">$new_val</span><span class="operator">);</span>
<span class="operator">};</span>
</pre>
<p>Here are <strong>FETCH</strong> and <strong>STORE</strong> callbacks for either an array or hash.
They do essentially the same thing as the scalar callbacks, but
provide a little more information.</p>
<pre>
<span class="keyword">my</span> <span class="variable">$fetch</span> <span class="operator">=</span> <span class="keyword">sub</span><span class="variable"> </span><span class="operator">{</span>
<span class="keyword">my</span><span class="operator">(</span><span class="variable">$self</span><span class="operator">,</span> <span class="variable">$key</span><span class="operator">)</span> <span class="operator">=</span> <span class="variable">@_</span><span class="operator">;</span>
<span class="keyword">my</span> <span class="variable">$val</span> <span class="operator">=</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Fetch</span><span class="operator">(</span><span class="variable">$key</span><span class="operator">);</span>
<span class="keyword">print</span> <span class="string">"In fetch callback, key=$key, val="</span><span class="operator">,</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Say</span><span class="operator">(</span><span class="variable">$val</span><span class="operator">);</span>
<span class="keyword">my</span> <span class="variable">$args</span> <span class="operator">=</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Args</span><span class="operator">(-</span><span class="variable">fetch</span><span class="operator">);</span>
<span class="keyword">print</span> <span class="string">", args=('"</span><span class="operator">,</span> <span class="keyword">join</span><span class="operator">(</span><span class="string">"', '"</span><span class="operator">,</span> <span class="variable">@$args</span><span class="operator">),</span> <span class="string">"')"</span> <span class="keyword">if</span> <span class="variable">$args</span><span class="operator">;</span>
<span class="keyword">print</span> <span class="string">".\n"</span><span class="operator">;</span>
<span class="variable">$val</span><span class="operator">;</span>
<span class="operator">};</span>
</pre>
<pre>
<span class="keyword">my</span> <span class="variable">$store</span> <span class="operator">=</span> <span class="keyword">sub</span><span class="variable"> </span><span class="operator">{</span>
<span class="keyword">my</span><span class="operator">(</span><span class="variable">$self</span><span class="operator">,</span> <span class="variable">$key</span><span class="operator">,</span> <span class="variable">$new_val</span><span class="operator">)</span> <span class="operator">=</span> <span class="variable">@_</span><span class="operator">;</span>
<span class="keyword">my</span> <span class="variable">$val</span> <span class="operator">=</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Fetch</span><span class="operator">(</span><span class="variable">$key</span><span class="operator">);</span>
<span class="variable">$new_val</span> <span class="operator">=</span> <span class="keyword">uc</span> <span class="variable">$new_val</span><span class="operator">;</span>
<span class="variable">$self</span><span class="operator">-></span><span class="variable">Store</span><span class="operator">(</span><span class="variable">$key</span><span class="operator">,</span> <span class="variable">$new_val</span><span class="operator">);</span>
<span class="keyword">print</span> <span class="string">"In store callback, key=$key, val="</span><span class="operator">,</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Say</span><span class="operator">(</span><span class="variable">$val</span><span class="operator">),</span>
<span class="string">", new_val="</span><span class="operator">,</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Say</span><span class="operator">(</span><span class="variable">$new_val</span><span class="operator">);</span>
<span class="keyword">my</span> <span class="variable">$args</span> <span class="operator">=</span> <span class="variable">$self</span><span class="operator">-></span><span class="variable">Args</span><span class="operator">(-</span><span class="variable">store</span><span class="operator">);</span>
<span class="keyword">print</span> <span class="string">", args=('"</span><span class="operator">,</span> <span class="keyword">join</span><span class="operator">(</span><span class="string">"', '"</span><span class="operator">,</span> <span class="variable">@$args</span><span class="operator">),</span> <span class="string">"')"</span> <span class="keyword">if</span> <span class="variable">$args</span><span class="operator">;</span>
<span class="keyword">print</span> <span class="string">".\n"</span><span class="operator">;</span>
<span class="variable">$new_val</span><span class="operator">;</span>
<span class="operator">};</span>
</pre>
<p>In all cases, the first parameter is a reference to the Watch object,
used to invoke the following class methods.</p>
<p>
</p>
<hr />
<h1><a name="methods">METHODS</a></h1>
<dl>
⌨️ 快捷键说明
复制代码Ctrl + C
搜索代码Ctrl + F
全屏模式F11
增大字号Ctrl + =
减小字号Ctrl + -
显示快捷键?