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Comment by donatj | Hacker News Reader

> There are no generics, and from what I understand for some odd reason will never be even though Hack forked from PHP and managed to add them?

The reason is pretty simple. Hack has a compilation step. PHP does not. Generics in an interpreted language means runtime errors, which are far less valuable and more troubling than compilation errors.

PHP’s loose typing + an offline static analyzer like phpstan will get you roughly the same result without the runtime errors.

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PHP doesn't have loose typing anymore, if you make a function parameter with a specific type:

    function test(bool $param) {}

You will get an runtime error if you call it with wrong type:

    Fatal error: Uncaught TypeError: test(): Argument #1 ($param) must be of type boolean

However generics are probably costly to typecheck runtime? I haven't studied the reason why there is not generics planned.

In a dynamic interpreted language there is no value of having generics over duck typing or omitting types altogether (and you can narrow down by specifying interfaces). Compiled languages generate a version of your function<T> for every T encountered in the codebase.

For completeness: other compiled languages elide that T and use the types in angulars only to emit errors during compilation. Also perfectly fine, but certainly not any help in absence of static compilation.

What a coincidence.

There's a video about generics in PHP, posted 2 hours ago: https://youtu.be/JtmRG5lCENA

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