Larastan: Cannot cast Ramsey\Uuid\UuidInterface to string.

[mkarnicki]

Got a message saying

Cannot cast Ramsey\Uuid\UuidInterface to string.

for this line:

$instance->uuid = (string) Str::uuid();

This works just fine, also see Laravel docs.

Thanks!

[ondrejmirtes]

The method should return Ramsey\Uuid\Uuid, not the interface.

On Mon, 23 Jul 2018 at 14:37, Michał Karnicki [e-mail]
wrote:

Got a message saying

Cannot cast Ramsey\Uuid\UuidInterface to string.

for this line:

$instance->uuid = (string) Str::uuid();

This works just fine, also see Laravel docs
https://laravel.com/docs/5.6/helpers#method-str-uuid.

Thanks!

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Ondřej Mirtes

[mkarnicki]

Well, the method may return Uuid instance, one that confirms to UuidInterface, but if it declared Uuid as return type, Ramsey could never change the underlying class without breaking other's code.

If he now decided to change the underlying class, yet conforming to the UuidInterface, the Laravel's Str::uuid() wouldn't break. Whereas if Ramsey decided to return some new 'UuidValue' class instance, if Str::uuid() declared returning an Uuid instance, it would break.

[ondrejmirtes]

PHPStan can (through a dynamic return type extension) say that the method always returns Uuid, without changing code of the library.

[mkarnicki]

Thanks for replying Ondrej. I'm not sure we understand each other.

What I'm saying is:

• Uuid implements UuidInterface
• UuidInterface has a toString method with a string return type hint.
• Laravel's Str::uuid() correctly returns an instance of a class that implements the UuidInterface contract, instead of the concrete class implementation Uuid.

I titled the issue report:

Cannot cast Ramsey\Uuid\UuidInterface to string.

which, I believe, is not true, because if the returned instance implements a toString method (and it does), it can be cast to string. Returning a contract (an interface), and not a concrete class, is a well known and widely used programming technique. There's ton of blog posts explaining why you should code to an interface.

What are you saying exactly?

[ondrejmirtes]

It’s a difference between having toString and __toString (which isn’t on
the interface).

On Mon, 23 Jul 2018 at 15:23, Michał Karnicki [e-mail]
wrote:

Thanks for replying Ondrej. I'm not sure we understand each other.

What I'm saying is:

• Uuid https://github.com/ramsey/uuid/blob/master/src/Uuid.php
  implements UuidInterface
  https://github.com/ramsey/uuid/blob/master/src/UuidInterface.php
• UuidInterface
  https://github.com/ramsey/uuid/blob/master/src/UuidInterface.php has
  a toString method with a string return type hint.
• Laravel's Str::uuid() correctly returns an instance of a class that
  implements the UuidInterface contract, instead of the concrete class
  implementation Uuid.

I titled the issue report:

Cannot cast RamseyUuidUuidInterface to string.

which, I believe, is not true, because if the returned instance implements
a toString method (and it does), it can be cast to string. Returning a
contract (an interface), and not a concrete class, is a well known and
widely used programming technique. There's ton of blog posts explaining why
you should code to an interface.

What are you saying exactly?

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Ondřej Mirtes

[mkarnicki]

You're right. In that case, I'd say that's a bug in RamseyUuid package then, not larastan, just a different king of bug than what you initially suggested. I'll leave it up to Nuno to close this or keep around.

[ondrejmirtes]

I don't think it's a bug in Uuid library itself - you just can't cast to string UuidInterface, it doesn't promise you that.

It's just a wrong assumption that everything that get's returned from Str::uuid can be cast to string which isn't right but isn't anybody's fault, really.

[mkarnicki]

You're right. The interface has a toString (non-magic) method that should be used instead. Thanks for teaching me something today.