Add support for yielding keys

Keys are yielded using the

    yield $key => $value

syntax. Currently this is implemented as a statement only and not as an
expression, because conflicts arise considering nesting and use in arrays:

    yield yield $a => $b;
    // could be either
    yield (yield $a) => $b;
    // or
    yield (yield $a => $b);

Once I find some way to resolve these conflicts this should be available
as an expression too.

Also the key yielding code is rather copy-and-past-y for the value yielding
code, so that should be factored out.

1 files changed, 26 insertions, 0 deletions

diff --git a/Zend/tests/generators/generator_with_keys.phpt b/Zend/tests/generators/generator_with_keys.phpt
new file mode 100644
index 0000000000..43e3e5ecf7
--- /dev/null
+++ b/Zend/tests/generators/generator_with_keys.phpt
@@ -0,0 +1,26 @@
+--TEST--
+Generators can also yield keys
+--FILE--
+<?php
+
+function *reverse(array $array) {
+    end($array);
+    while (null !== $key = key($array)) {
+        yield $key => current($array);
+        prev($array);
+    }
+}
+
+$array = [
+    'foo' => 'bar',
+    'bar' => 'foo',
+];
+
+foreach (reverse($array) as $key => $value) {
+    echo $key, ' => ', $value, "\n";
+}
+
+?>
+--EXPECT--
+bar => foo
+foo => bar