Jordan Delong
363d1bb20f
This change is mostly for FB internal organizational reasons. Building is not effected beyond the fact that the target now lands in hphp/hhvm/hhvm rather than src/hhvm/hhvm.
61 linhas
1.8 KiB
Plaintext
61 linhas
1.8 KiB
Plaintext
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<h2>yield and generator</h2>
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This feature requires the [[index.php?file=options.compiler | compiler option]]
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EnableHipHopSyntax=true, or interpreter option Eval.EnableHipHopSyntax=true.
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HipHop extends PHP to include Python and C#-style generators. If you're
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unfamiliar with the concept, see
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[[http://docs.python.org/tutorial/classes.html#generators | the Python docs]].
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As in Python, the <i>yield</i> keyword marks the enclosing function as a
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generator:
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function foo() {
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$a = 123;
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yield $a;
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$a = 456;
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yield $a;
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}
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foreach (foo() as $a) {
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print "$a,";
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}
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The above program outputs "123,456,". To abort a generator sequence, use "yield
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break".
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function bar() {
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$a = 123;
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// this will stop the "foreach" immediately without any value returned
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if ($abort) yield break;
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yield $a;
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$a = 456;
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yield $a;
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}
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Generators must observe the following restrictions:
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- Generators are <b>not recursive</b>. In the above example, foo() cannot call
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foo() while iterating.
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- Generators are <b>called once</b>: foo() cannot be called again after it's
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done iterating.
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- Do not call the rewind() method of the objects (of class Iterator) returned by
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iterator functions.
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Also, yield in HipHop also supports passing a value from outside of the
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generator.
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function foo() {
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$a = yield 5;
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yield $a + 1;
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}
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From outside the generator, instead of resuming the generator with
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Continuation::next(), one can call Continuation::send() to pass a value, which
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will be assigned to $a, back into the generator.
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Note that the yield expression in the above example is not really an expression;
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it can only appear on its own on the RHS of an assignment statement. This is to
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avoid the complicated evaluation order problem in bizarre expressions like
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"($a = yield 5) * (yield $a + 3) - ($a = yield 4)".
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