Conditional return via static lookup array

[ruudk]

Bug report

I'm trying to let PHPStan understand the following code using a static TYPES array to lookup a given type.

class HelloWorld
{
    private const TYPES = [
        'foo' => DateTime::class,
        'bar' => DateTimeImmutable::class,
    ];

    /**
     * @template T of key-of<self::TYPES>
     * @param T $type
     * @return self::TYPES[T]
     */
    public static function get(string $type) : ?object
    {
        $class = self::TYPES[$type] ?? null;
        if ($class === null) {
            return null;
        }

        return new $class('now');
    }
}

But whatever I try, it seems I cannot tell PHPStan that the return type will be an instance of the value from the self::TYPES constant array.

I also tried:

@return (self::TYPES[T] is defined ? self::TYPES[T] : null)

Code snippet that reproduces the problem

https://phpstan.org/r/e086655c-9d6d-4ed8-9f80-c3e3f33bdc9b

Expected output

I expect it to correctly understand the type.

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[ondrejmirtes]

This gets you close: https://phpstan.org/r/ba879058-ecef-459c-b7ff-69e03be2ac1f

The problem is that in the array you have class-strings but you want objects. I'm not sure if it can currently be solved, most likely we'd need some kind of type that lets us go from class-string<T> to T.

[ruudk]

Thanks, that already looks better.

Couldn't we use object<T> for this? Like: @return (K is key-of<M> ? object<M[K]> : null)

[phpstan-bot]

@ruudk After the latest push in 1.11.x, PHPStan now reports different result with your code snippet:

@@ @@
 15: PHPDoc tag @return with type array<string, string> is incompatible with native type object|null.
 17: Dumped type: T of 'bar'|'foo' (method HelloWorld::get(), argument)
+18: Offset T of 'bar'|'foo' on array{foo: 'DateTime', bar: 'DateTimeImmutable'} on left side of ?? always exists and is not nullable.
+19: Strict comparison using === between 'DateTime'|'DateTimeImmutable' and null will always evaluate to false.
 27: Dumped type: object|null
 30: Dumped type: object|null

Full report

Line	Error
15	`PHPDoc tag @return with type array<string, string> is incompatible with native type object
17	`Dumped type: T of 'bar'
18	`Offset T of 'bar'
19	`Strict comparison using === between 'DateTime'
27	`Dumped type: object
30	`Dumped type: object

[ruudk]

It's getting better but still not working properly: https://phpstan.org/r/e9ae422d-ab7f-400e-99df-f213c1022b09

[rvanvelzen]

This patch would create an object<...> type as mentioned in a comment: https://gist.github.com/rvanvelzen/5bd097289e857cc8590adf278e77def5

[ruudk]

Thanks!

@ondrejmirtes is this something you would accept as a PR?

@rvanvelzen would you want to submit this as a PR? If you don't want to I can do it with your code. But you did the work obviously 😄

[ondrejmirtes]

Maybe I'm having some kind of friday afternoon brain fart but what's the difference between T and object<T>? Can you post a full example about how it should behave?

[ruudk]

The issue is that T is class-string, not an object of T. Introducing object would allow to type that.

#9704 (comment)

[ondrejmirtes]

What about new<T> instead? It'd make it more obvious. object<T> is not that intuitive I think.

[ruudk]

That's even better!

[ondrejmirtes]

Good news is: we can do it because a class cannot be named new: https://3v4l.org/YhCv3

[phpstan-bot]

@ruudk After the latest push in 1.11.x, PHPStan now reports different result with your code snippet:

@@ @@
-15: PHPDoc tag @return with type array<string, string> is incompatible with native type object|null.
+15: PHPDoc tag @return with type array{foo: 'DateTime', bar: 'DateTimeImmutable'}[T] is incompatible with native type object|null.
 17: Dumped type: T of 'bar'|'foo' (method HelloWorld::get(), argument)
+18: Offset T of 'bar'|'foo' on array{foo: 'DateTime', bar: 'DateTimeImmutable'} on left side of ?? always exists and is not nullable.
+19: Strict comparison using === between 'DateTime'|'DateTimeImmutable' and null will always evaluate to false.
 27: Dumped type: object|null
 30: Dumped type: object|null

Full report

Line	Error
15	`PHPDoc tag @return with type array{foo: 'DateTime', bar: 'DateTimeImmutable'}[T] is incompatible with native type object
17	`Dumped type: T of 'bar'
18	`Offset T of 'bar'
19	`Strict comparison using === between 'DateTime'
27	`Dumped type: object
30	`Dumped type: object

[phpstan-bot]

@ruudk After the latest push in 1.11.x, PHPStan now reports different result with your code snippet:

@@ @@
-18: PHPDoc tag @return with type array<string, string> is incompatible with native type object|null.
+18: PHPDoc tag @return with type array{foo: 'DateTime', bar: 'DateTimeImmutable'}[T] is incompatible with native type object|null.
 20: Dumped type: T of 'bar'|'foo' (method HelloWorld::get(), argument)
 22: Dumped type: 'DateTime'|'DateTimeImmutable'
 28: Dumped type: object|null
 31: Dumped type: object|null

Full report

Line	Error
18	`PHPDoc tag @return with type array{foo: 'DateTime', bar: 'DateTimeImmutable'}[T] is incompatible with native type object
20	`Dumped type: T of 'bar'
22	`Dumped type: 'DateTime'
28	`Dumped type: object
31	`Dumped type: object

[ondrejmirtes]

Fixed phpstan/phpstan-src#3050