How to extract nullable type

[lud]

Hi,

I would like to build this function:

function bang($value)
{
    if (null === $value) throw ...
   return $value;
}

And I would call it like this:

class A {
    public function maybeString(): ?string
    {
        if (...) return null;
        else return 'hello';
    }
    
    public function maybeThis(): ?self
    {
        if (...) return null;
        else return $this;
    }
}

bang($a->maybeString()); // @return string
bang($a->maybeThis()); // @return A

So I would like to write a typespec for the bang function, i.e. transforming a type ?T into T.

Is it possible to write such a typespec ?

Thank you.

[ondrejmirtes]

This should work but currently doesn't: https://phpstan.org/r/15a41cbf-20e8-409e-898f-19afcf823750

[lud]

Thanks @ondrejmirtes that was my first approach too but yes, not working.

I rewrote your example to make it show the problem better (at least to my taste edit: no, I see where yours shows the problem now) : https://phpstan.org/r/38a882d5-d57b-4927-9acd-43a4a0213e99

[lud]

/**
 * @template T
 * @param T|null $value
 * @return T
 */

When you say it should work, does it means that if the type of the passed argument is ?string, phpstan knows that by mapping T|null to ?string, T is string ?

So what happens there is just that T is mapped to ?string and so @return T logically tells that the function returns ?string. Am I right?

[ondrejmirtes]

It has to be accounted for in the bugfix.

[lud]

But I am not sure that is correct.

For instance imagine another function where param is T|int, and the passed argument is string|int, should return T mean that the function will only return string?

edit: or is it correct only because of the if (null === $value) part ?

[ondrejmirtes]

I’m not sure, that would have to investigated and discussed.

[lud]

Ok :)

I hope that will interest someone because I do not have the required skills right now :S

[enumag]

@ondrejmirtes Hmm... I assume this won't be an easy one eh? Ofc it's not just null, the same can be done with other types. So it's most likely a non-trivial generics problem.

[ondrejmirtes]

I think it's a matter of touching UnionType::inferTemplateTypes() and UnionType::inferTemplateTypesOn(). And yeah, the logic has to account for some edge cases that need to continue to work...

[phpstan-bot]

@ondrejmirtes After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-28: Strict comparison using === between string|null and 1 will always evaluate to false.
-29: Strict comparison using === between A|null and 1 will always evaluate to false.
+28: Strict comparison using === between string and 1 will always evaluate to false.
+29: Strict comparison using === between A and 1 will always evaluate to false.

Full report

Line	Error
28	Strict comparison using === between string and 1 will always evaluate to false.
29	Strict comparison using === between A and 1 will always evaluate to false.

[phpstan-bot]

@lud After the latest commit in dev-master, PHPStan now reports different result with your code snippet:

@@ @@
-32: Parameter #1 $str of function acceptString expects string, string|null given.
-33: Parameter #1 $str of function acceptString expects string, string|null given.
+32: Parameter #1 $str of function acceptString expects string, string|null given.

Full report

Line	Error
32	`Parameter #1 $str of function acceptString expects string, string

[ondrejmirtes]

Fixed: phpstan/phpstan-src@a1b7b38

[lud]

Great, thank you!

[github-actions]

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