Substitute type parameters when checking overridden members

[lars-reimann]

Is your feature request related to a problem?

isSubtypeOf should only support its strict mode. This, however, requires that we always substitute type parameters before type checking. This is also needed when checking whether an overriding method is compatible to an overridden method:

class MyClass1 {
    fun f(p: Int) -> r: Int
}

class MyClass2 sub MyClass1 {
    fun f<T>(p: T) -> r: T
}

In the current strict type checking mode, we get an error:

Overriding member does not match the overridden member:
- Expected type: (p: Int) -> (r: Int)
- Actual type:   (p: T) -> (r: T)

Currently, we only substitute type parameters of the containing class, but not type parameters of methods.

Desired solution

1. Compute substitutions for the type parameters in the parameter list of the overriding method by comparing it to the parameter list of the overridden method.
2. Apply those substitutions to the type of the overriding method.
3. Check whether the type from step 2 can be assigned to the type of the overridden method.

Possible alternatives (optional)

Don't allow type parameters on instance methods? They seem mostly useful for static method/global functions.

This does not help, since the overriding method might still use type parameters of the class.

Screenshots (optional)

No response

Additional Context (optional)

No response

[lars-reimann]

🎉 This issue has been resolved in version 0.8.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• v0.8.0
• GitHub release

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