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Subject: Re: [PHP-DEV] Basic Type Alias
From: marc@mabe.berlin (Marc)

Hi,

On 26.10.23 08:37, Oladoyinbo Vincent wrote:
> Greetings to you all,
>
> I will like to submit an RFC on introducing type alias to php.
>
> Even though Generics won't or never be introduced to PHP, personally i will
> like php to add the type alias feature.
>
> Type aliases provide a mechanism to create more descriptive and readable
> type hints in PHP code. This enhancement will improve code readability and
> maintainability and also to promote type reusability.
>
>
> Motivation:
>
> The motivation behind introducing type aliases is to:
>
> 1. Enhance code readability by allowing developers to use meaningful type
> hint names.
> 2. Improve code maintainability by reducing the likelihood of type hint
> updates throughout the codebase.
> 3. Encourage the adoption of best practices for type hinting.
>
>
> Proposal:
>
> Syntax:
>
> Type aliases will be declared using the `type` or `typealias` keyword,
> followed by the alias name, an equal sign (`=`), and the type it is aliased
> to.
>
>
> Sample:
>
> ```
> type MyType = string;
>
> // or
>
> typealias MyType = string;
>
>
> // Advance
>
> type MyType = string|null;
>
> // or
>
> type MyType = [string, null];
>
> ```
>
>
> Usage:
>
> Type aliases can be used in parameter and return type hints as follows:
>
> ```
>
> function greetings(MyType $message): string {
>
>      // Implementation
>
> }
>
> greetings(1); // TypeError
>
> ```
>
> Since this is just a basic feature, Type aliases Inheritance (compound
> type) may not be added, since we are not digging deeper into generics :).
>
>
>
> References:
>
> https://docs.python.org/3/glossary.html#term-type-alias
>
> https://doc.rust-lang.org/beta/reference/items/type-aliases.html
>
> https://www.typescriptlang.org/docs/handbook/typescript-in-5-minutes-func.html#type-aliases
>
>
> So, What do you think?
>
I would love to see type aliases added to PHP but I think it would be 
very less useful if it's scoped per file only.

Like `type UserId = string;` in it's self already improves readability 
but only if reusable by different files and because of that a big 
question about autoloading/performance comes in here as well.


About the syntax: I think this should be consistent with how we declare 
types right now ...
`type UserId: string;` instead of `type UserId = string;`


Another question is how the type annotations will behave if the aliased 
type is hinted:

type UserId: string;

function test(UserId $userId): string {
     return $userId;
}

test("its-me");


Also, would it be possible to handle types as specialized classes 
including namespaces, helper functions and usable with reflection?

type UserId: string;

type OtherId: UserId;

UserId::base // "string"

OtherId::base // "string"

UserId::nullable // false

UserId::isValid(mixed $var): bool

$refl = ReflectionClass(UserId::class);
$refl = ReflectionType::from(UserId::class);

...


Best,
Marc