File: C:/Ruby27-x64/share/doc/ruby/html/Continuation.html
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<li ><a href="#method-i-5B-5D">#[]</a>
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<h1 id="class-Continuation" class="class">
class Continuation
</h1>
<section class="description">
<p><a href="Continuation.html"><code>Continuation</code></a> objects are generated by <a href="Kernel.html#method-i-callcc"><code>Kernel#callcc</code></a>, after having +require+d <em>continuation</em>. They hold a return address and execution context, allowing a nonlocal return to the end of the <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> block from anywhere within a program. Continuations are somewhat analogous to a structured version of C's <code>setjmp/longjmp</code> (although they contain more state, so you might consider them closer to threads).</p>
<p>For instance:</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">"continuation"</span>
<span class="ruby-identifier">arr</span> = [ <span class="ruby-string">"Freddie"</span>, <span class="ruby-string">"Herbie"</span>, <span class="ruby-string">"Ron"</span>, <span class="ruby-string">"Max"</span>, <span class="ruby-string">"Ringo"</span> ]
<span class="ruby-identifier">callcc</span>{<span class="ruby-operator">|</span><span class="ruby-identifier">cc</span><span class="ruby-operator">|</span> <span class="ruby-identifier">$cc</span> = <span class="ruby-identifier">cc</span>}
<span class="ruby-identifier">puts</span>(<span class="ruby-identifier">message</span> = <span class="ruby-identifier">arr</span>.<span class="ruby-identifier">shift</span>)
<span class="ruby-identifier">$cc</span>.<span class="ruby-identifier">call</span> <span class="ruby-keyword">unless</span> <span class="ruby-identifier">message</span> <span class="ruby-operator">=~</span> <span class="ruby-regexp">/Max/</span>
</pre>
<p><em>produces:</em></p>
<pre class="ruby"><span class="ruby-constant">Freddie</span>
<span class="ruby-constant">Herbie</span>
<span class="ruby-constant">Ron</span>
<span class="ruby-constant">Max</span>
</pre>
<p>Also you can call callcc in other methods:</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">"continuation"</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">g</span>
<span class="ruby-identifier">arr</span> = [ <span class="ruby-string">"Freddie"</span>, <span class="ruby-string">"Herbie"</span>, <span class="ruby-string">"Ron"</span>, <span class="ruby-string">"Max"</span>, <span class="ruby-string">"Ringo"</span> ]
<span class="ruby-identifier">cc</span> = <span class="ruby-identifier">callcc</span> { <span class="ruby-operator">|</span><span class="ruby-identifier">cc</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cc</span> }
<span class="ruby-identifier">puts</span> <span class="ruby-identifier">arr</span>.<span class="ruby-identifier">shift</span>
<span class="ruby-keyword">return</span> <span class="ruby-identifier">cc</span>, <span class="ruby-identifier">arr</span>.<span class="ruby-identifier">size</span>
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">def</span> <span class="ruby-identifier ruby-title">f</span>
<span class="ruby-identifier">c</span>, <span class="ruby-identifier">size</span> = <span class="ruby-identifier">g</span>
<span class="ruby-identifier">c</span>.<span class="ruby-identifier">call</span>(<span class="ruby-identifier">c</span>) <span class="ruby-keyword">if</span> <span class="ruby-identifier">size</span> <span class="ruby-operator">></span> <span class="ruby-value">1</span>
<span class="ruby-keyword">end</span>
<span class="ruby-identifier">f</span>
</pre>
<p>This (somewhat contrived) example allows the inner loop to abandon processing early:</p>
<pre class="ruby"><span class="ruby-identifier">require</span> <span class="ruby-string">"continuation"</span>
<span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span>
<span class="ruby-keyword">for</span> <span class="ruby-identifier">i</span> <span class="ruby-keyword">in</span> <span class="ruby-value">0</span><span class="ruby-operator">..</span><span class="ruby-value">4</span>
<span class="ruby-identifier">print</span> <span class="ruby-node">"#{i}: "</span>
<span class="ruby-keyword">for</span> <span class="ruby-identifier">j</span> <span class="ruby-keyword">in</span> <span class="ruby-identifier">i</span><span class="ruby-operator">*</span><span class="ruby-value">5</span><span class="ruby-operator">...</span>(<span class="ruby-identifier">i</span><span class="ruby-value">+1</span>)<span class="ruby-operator">*</span><span class="ruby-value">5</span>
<span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span>() <span class="ruby-keyword">if</span> <span class="ruby-identifier">j</span> <span class="ruby-operator">==</span> <span class="ruby-value">17</span>
<span class="ruby-identifier">printf</span> <span class="ruby-string">"%3d"</span>, <span class="ruby-identifier">j</span>
<span class="ruby-keyword">end</span>
<span class="ruby-keyword">end</span>
}
<span class="ruby-identifier">puts</span>
</pre>
<p><em>produces:</em></p>
<pre>0: 0 1 2 3 4
1: 5 6 7 8 9
2: 10 11 12 13 14
3: 15 16</pre>
</section>
<section id="5Buntitled-5D" class="documentation-section">
<section id="public-instance-5Buntitled-5D-method-details" class="method-section">
<header>
<h3>Public Instance Methods</h3>
</header>
<div id="method-i-5B-5D" class="method-detail ">
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<span class="method-callseq">
cont[args, ...]
</span>
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<div class="method-description">
<p>Invokes the continuation. The program continues from the end of the <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> block. If no arguments are given, the original <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> returns <code>nil</code>. If one argument is given, <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> returns it. Otherwise, an array containing <em>args</em> is returned.</p>
<pre class="ruby"><span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span> } <span class="ruby-comment">#=> nil</span>
<span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span> <span class="ruby-value">1</span> } <span class="ruby-comment">#=> 1</span>
<span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span> <span class="ruby-value">1</span>, <span class="ruby-value">2</span>, <span class="ruby-value">3</span> } <span class="ruby-comment">#=> [1, 2, 3]</span>
</pre>
<div class="method-source-code" id="5B-5D-source">
<pre>static VALUE
rb_cont_call(int argc, VALUE *argv, VALUE contval)
{
rb_context_t *cont = cont_ptr(contval);
rb_thread_t *th = GET_THREAD();
if (cont_thread_value(cont) != th->self) {
rb_raise(rb_eRuntimeError, "continuation called across threads");
}
if (cont->saved_ec.protect_tag != th->ec->protect_tag) {
rb_raise(rb_eRuntimeError, "continuation called across stack rewinding barrier");
}
if (cont->saved_ec.fiber_ptr) {
if (th->ec->fiber_ptr != cont->saved_ec.fiber_ptr) {
rb_raise(rb_eRuntimeError, "continuation called across fiber");
}
}
rollback_ensure_stack(contval, th->ec->ensure_list, cont->ensure_array);
cont->argc = argc;
cont->value = make_passing_arg(argc, argv);
cont_restore_0(cont, &contval);
return Qnil; /* unreachable */
}</pre>
</div>
</div>
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<div id="method-i-call" class="method-detail ">
<div class="method-heading">
<span class="method-callseq">
call(args, ...)
</span>
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</div>
<div class="method-description">
<p>Invokes the continuation. The program continues from the end of the <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> block. If no arguments are given, the original <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> returns <code>nil</code>. If one argument is given, <a href="Kernel.html#method-i-callcc"><code>callcc</code></a> returns it. Otherwise, an array containing <em>args</em> is returned.</p>
<pre class="ruby"><span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span> } <span class="ruby-comment">#=> nil</span>
<span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span> <span class="ruby-value">1</span> } <span class="ruby-comment">#=> 1</span>
<span class="ruby-identifier">callcc</span> {<span class="ruby-operator">|</span><span class="ruby-identifier">cont</span><span class="ruby-operator">|</span> <span class="ruby-identifier">cont</span>.<span class="ruby-identifier">call</span> <span class="ruby-value">1</span>, <span class="ruby-value">2</span>, <span class="ruby-value">3</span> } <span class="ruby-comment">#=> [1, 2, 3]</span>
</pre>
<div class="method-source-code" id="call-source">
<pre>static VALUE
rb_cont_call(int argc, VALUE *argv, VALUE contval)
{
rb_context_t *cont = cont_ptr(contval);
rb_thread_t *th = GET_THREAD();
if (cont_thread_value(cont) != th->self) {
rb_raise(rb_eRuntimeError, "continuation called across threads");
}
if (cont->saved_ec.protect_tag != th->ec->protect_tag) {
rb_raise(rb_eRuntimeError, "continuation called across stack rewinding barrier");
}
if (cont->saved_ec.fiber_ptr) {
if (th->ec->fiber_ptr != cont->saved_ec.fiber_ptr) {
rb_raise(rb_eRuntimeError, "continuation called across fiber");
}
}
rollback_ensure_stack(contval, th->ec->ensure_list, cont->ensure_array);
cont->argc = argc;
cont->value = make_passing_arg(argc, argv);
cont_restore_0(cont, &contval);
return Qnil; /* unreachable */
}</pre>
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