Add support for generic methods

[thekid]

This pull request adds the possibility to define methods with their own generic type arguments. Implemented via inserting typeargs as first parameter and __call().

Example

Declaration:

use lang\Generic;

#[Generic(self: 'T')]
class ListOf {
  public private(set) $elements= [];

  #[Generic(params: 'T...')]
  public function __construct(... $args) {
    $this->elements= $args;
  }

  #[Generic(self: 'M', params: 'function(T): M', return: 'self<M>')]
  public function map($map) {
    $m= create("new self<$M>");
    foreach ($this->elements as $element) {
      $m->elements[]= $map($element);
    }
    return $m;
  }
}

Calls:

$list= create('new ListOf<string>', 'Hello', 'World!');

// Returns a ListOf<int>
$lengths= $list->{'map<int>'}(strlen(...));

// Contains [5, 6]
$lengths->elements;

Implementation status

• Proof of concept
• Argument verification
• Reflection

See also

• Support generic methods xp-lang/xp-generics#3
• https://gist.github.com/hollyschilling/abcdd66dae18437f56bf56e350860b48

[thekid]

Reflection

For C#, we need to use MakeGenericMethod:

using System;
using System.Reflection;

public class Sample
{
    public void GenericMethod<T>()
    {
      Console.WriteLine($"GenericMethod<{typeof(T).Name}> invoked");
    }
}

class Program
{
    static void Main()
    {
        var instance = new Sample();
        Type runtimeType = typeof(string);
        
        // 1. Get MethodInfo for the generic method definition
        MethodInfo method = typeof(Sample).GetMethod(nameof(Sample.GenericMethod));
        
        // 2. Construct the generic method with the runtime type
        MethodInfo constructed = method.MakeGenericMethod(runtimeType);
        
        // 3. Invoke it on the instance
        constructed.Invoke(instance, null);
    }
}

See https://stackoverflow.com/questions/232535/how-do-i-call-a-generic-method-using-a-type-variable