Change yield interpolation behaviour

Yes you are right. The same thing happens if you put a function there.

function hi(): string
{
    return ‘World’;
}
 
echo <<<MSG
    Hello ${hi()}
MSG;
// Warning: Undefined variable $World!

 
For some reason, I did not take this case into account.
 
Although it seems to me such semantics are old and require removal from the language, I admit that there is code that uses it and changing the behavior will break a lot. Ideally, I would like to see a similar behavior:

echo "Hello ${ $var }"; // Hello World
echo "Hello ${ 'Wo' . 'rld' }"; // same
echo "Foo ${ some_foo(42) }";
echo "Foo ${ 23 + 42 }"; 
echo "Some ${ ClassName::method() >> 2 ?? $any }";
// etc

Пятница, 8 октября 2021, 12:22 +03:00 от Nikita Popov nikita.ppv@gmail.com:
 

 

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.

This doesn't really have anything to do with yield. ${expr} is PHP's
general variable-variable syntax, which looks up the variable with name
returned by expr. The syntax also works inside strings in the form of
"${expr}". Using "${yield $v}" is just a specific instance of the general
pattern following the same rules. (This syntax has a special case that
should be deprecated: "${label}" will be interpreted the same as "$label"
instead, which is inconsistent with how it works everywhere else. This is
also why ${yield} without argument will not perform a yield and instead
look for a variable called $yield.)

PHP unfortunately doesn't have a general expression interpolation syntax,
you can only interpolate variables and certain variable-like constructs.

Regards,
Nikita
 
 
--
Kirill Nesmeyanov