Builder and hassers or generics

[robotomarvin]

Hi, I'm trying to achieve type narrowing of the output from a builder.
For example

$entity = (new Builder(5))->setName("name")->create();
\PHPStan\dumpType($entity->getName());

I know that getName would not be null due to setName call on builder.
(full example https://phpstan.org/r/4a2c6d56-8c58-47d5-b996-d5ec70df5c72)

My idea was to solve this using generics. In my case I would not call getName when setName was not previously called so I can change that method to always return nonnullable value and throw exception otherwise. But I still want the check, that I can call this method safely. I tried separation the entity into interfaces and modify the return type of the builder to BaseEntity&EntityWithName, from the outside this works nicely. But in the builder phpstan reports Type Entity is not always the same as T. It breaks the contract for some argument types, typically subtypes. ant that is true, I could instantiate the builder as something like Builder<DateTime> and that would seem to be valid. I'm lurking for something like @template T partialof Entity could something like that be achieved?
(full example https://phpstan.org/r/02d1c5a8-2890-44fa-a3e0-2f102fe26caa)

[ondrejmirtes]

Hi,

1. @return above the constructor does not achieve anything.
2. Your code is mostly fine. PHPStan rightfully complains on line 57 because you don't work with T at all in the method body so T can really be different than Entity.

But if the builder works alright from the outside type-wise I'd just use it like this while ignoring or avoiding the error in create(). PHPStan itself employs a similar pattern here https://github.com/phpstan/phpstan-src/blob/1.11.x/src/Rules/RuleErrorBuilder.php and it works around this problem with /** @var class-string<T> $className */ in the build() method.

[robotomarvin]

Thanks for quick response, nice to see similar thing being done, I felt like I'm doing something wrong.