Type parameters for class_alias

[klimick]

There are currently no true type aliases in PHP. Except class_alias: https://3v4l.org/kVf0M But class_alias cannot have any type parameters.

I can't write code like this:

<?php

declare(strict_types=1);

/**
 * @template K
 * @template V
 */
final class Map {
    /**
     * @param list<array{K, V}> $paris
     */
    public function __construct(
        array $paris = [],
    ) {
    }
}

final class Uuid {}

/**
 * @template T
 * @class-alias Map<Uuid, T>
 */
class_alias(Map::class, UuidMap::class);

/**
 * @param UuidMap<int> $_uuidMap
 */
function gimmeUuidMap(UuidMap $_uuidMap): void
{
}

(on psalm.dev: https://psalm.dev/r/73fbe474ad)

It was great to support this in the psalm! I can try to do this. Do you want to stop me?

[psalm-github-bot[bot]]

I found these snippets:

https://psalm.dev/r/73fbe474ad

<?php

declare(strict_types=1);

/**
 * @template K
 * @template V
 */
final class Map {
    /**
     * @param list<array{K, V}> $paris
     */
    public function __construct(
        array $paris = [],
    ) {
    }
}

final class Uuid {}

/**
 * @template T
 * @class-alias Map<Uuid, T>
 */
class_alias(Map::class, UuidMap::class);

/**
 * @param UuidMap<int> $_uuidMap
 */
function gimmeUuidMap(UuidMap $_uuidMap): void
{
}

Psalm output (using commit 3600d51):

ERROR: MissingTemplateParam - 28:11 - Map has missing template params, expecting 2

[weirdan]

To me, it looks way more complex than https://psalm.dev/r/75732c0bf7

[psalm-github-bot[bot]]

I found these snippets:

https://psalm.dev/r/75732c0bf7

<?php

declare(strict_types=1);

/**
 * @template K
 * @template V
 */
class Map {
    /**
     * @param list<array{K, V}> $pairs
     */
    public function __construct(
        array $pairs = [],
    ) {
    }
}

final class Uuid {}

/**
 * @template T
 * @extends Map<Uuid,T>
 */
final class UuidMap extends Map {}

/**
 * @param UuidMap<int> $_uuidMap
 */
function gimmeUuidMap(UuidMap $_uuidMap): void
{
}

Psalm output (using commit 3600d51):

No issues!

[klimick]

@weirdan With your code, I can't pass Map<Uuid, int> to gimmeUuidMap function: https://psalm.dev/r/3b5a4a7d83 With class_alias it should be possible.

In our codebase we usually use Set<Uuid> or Vector<Uuid>. It was nice for our eyes to get real type aliases and make UuidVector and UuidSet. In many places we could avoid writing phpdoc at all.

This is a "nice to have, but not required" functionality.

[psalm-github-bot[bot]]

I found these snippets:

https://psalm.dev/r/3b5a4a7d83

<?php

declare(strict_types=1);

/**
 * @template K
 * @template V
 */
class Map {
    /**
     * @param list<array{K, V}> $pairs
     */
    public function __construct(
        array $pairs = [],
    ) {
    }
}

final class Uuid {}

/**
 * @template T
 * @extends Map<Uuid,T>
 */
final class UuidMap extends Map {}

/**
 * @param UuidMap<int> $_uuidMap
 */
function gimmeUuidMap(UuidMap $_uuidMap): void
{
}

/** @var Map<Uuid, int> */
$uuidMap = new Map();
gimmeUuidMap($uuidMap);

Psalm output (using commit 3600d51):

ERROR: ArgumentTypeCoercion - 36:14 - Argument 1 of gimmeUuidMap expects UuidMap<int>, but parent type Map<Uuid, int> provided

[weirdan]

Ah, I see. I would probably reject such a PR to Psalm. Alias handling in Psalm has its issues, and so do generics. Combining them sounds like a maintenance pain for a little gain.