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Date: Fri, 8 Oct 2021 11:55:08 +0300
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Subject: Change yield interpolation behaviour
From: nesk@xakep.ru (Nesmeyanov Kirill)

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()];

}

```

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?