谁的PHP的YIELD-> send（）有效？

Question

function yielding()
{
    for ($i = 0; $i < 10; $i++) {
        var_dump(yield);
    }
}

$y = yielding();

foreach ($y as $val) {
    $y->send('foo');
}

output:

string(3) "foo"
NULL
string(3) "foo"
NULL
string(3) "foo"
NULL
string(3) "foo"
NULL
string(3) "foo"

i expected the output to be: 10 time string(3) "foo", but instead the output is one NULL and one string(3) "foo" (9 times). why is it? does generator->send() skip one iteratoration?

Answer 1

yield is used for both sending and receiving values inside the generator. From the Generator RFC: If nothing was sent (e.g. during foreach iteration) null is returned.

So in your code, the generator is resumed twice:

1. once for ($y as $val) -- yield returns null inside the generator
2. once for $y->send('foo') -- yield returns 'foo' inside the generator

When I ran your code I got 10 lines of output, ending with NULL

string(3) "foo"
NULL
...
string(3) "foo"
NULL