Change yield interpolation behaviour

Пятница, 8 октября 2021, 12:14 +03:00 от Kirill Nesmeyanov nesk@xakep.ru:
 

 
Hello Internals!

At the moment, there is a feature/bug in the PHP that allows to use
interpolation of generators.

$code = <<<EXAMPLE
     Hello ${yield}
EXAMPLE;

I suspect that initially this functionality was not thought out, but it
partially works, which allows you to implement useful functionality.

[$query, $params] = sql(fn() => <<<SQL
     SELECT * FROM users WHERE id = ${yield 42} OR id = ${yield 0xDEADBEEF}
SQL);

// Expected
// $query = "SELECT * FROM users WHERE id = ? OR id = ?"
// $params = [ 42, 0xDEADBEEF ]

When I say that the functionality was not thought out initially, I mean
the behavior of generators within strings. For example, the following
code, which should (seemingly) implement this functionality:

function sql(\Closure $expr)
{
     [$generator, $params] = [$expr(), $params];

     while ($generator->valid()) {
        $params[] = $generator->current(); // Get the value from "yield"
        $generator->send('?'); // Insert placeholder
     }

     return [$generator->getReturn(), $params];
}

Causes an error:

Warning: Undefined variable $?

That is, the expression "${yield 42}" expects back not the result of
this expression, but the name of the variable. Therefore, a complete and
workable implementation of such a functionality is as follows:
https://gist.github.com/SerafimArts/2e7702620480fbce6c24bc87bfb9cb0e

I think it makes sense to do something about it.
I have two suggestions:

1. Forbid using "yield" inside strings
2. Expect not a variable name as a result of this expression, but a
   substitution value.

What do you think?

Kirill Nesmeyanov
 
I apologize for the mail duplication. I did not see it receiving on the mailing list (https://news-web.php.net/php.internals) so I sent it again. However, the first came through.
 
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Kirill Nesmeyanov