Support for generic type constraints in function signatures #10296
Description
Feature request
Concerning this discussion, here is a feature request (I'm not very sure about the name of the feature itself)
After a few tries and thanks to the help of Copilot (this is my first time working with Hacklang) I've been able to replicate the feature request:
class Ref<T>
{
public function __construct(private T $value)
{
}
public function zip<TOther>(Ref<TOther> $other) : Ref<(T, TOther)>
{
return new Ref(tuple($this->value, $other->value));
}
public function unzip<T1, T2>() : (Ref<T1>, Ref<T2>) where T = (T1, T2)
{
return tuple(
new Ref($this->value[0]),
new Ref($this->value[1]),
);
}
}
function example1(): void
{
$a = new Ref(1); // Ref<int>
$b = new Ref('foo'); // Ref<string>
$c = $a->zip($b); // Ref<(int, string)>
$d = $c->unzip(); // (Ref<int>, Ref<string>)
}
function example2(): void
{
$a = new Ref(1); // Ref<int>
// Typing[4323] A where type constraint is violated here [1]
// -> This is the method with where type constraints [2]
// -> Expected (_, _) [3]
// -> But got int [4]
$b = $a->unzip();
}
function example3(): void
{
$a = new Ref(tuple(1, tuple(false, 4.20))); // Ref<(int, (bool, float))>
$b = $a->unzip(); // (Ref<int>, Ref<(bool, float)>)
// Typing[4323] A where type constraint is violated here [1]
// -> This is the method with where type constraints [2]
// -> Expected (_, _) [3]
// -> But got int [4]
$c = $b[0]->unzip();
$d = $b[1]->unzip(); // (Ref<bool>, Ref<float>)
}I still think this is similar to @psalm-if-this-is in practice, as it's a way to set the template type based on a condition.
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