Open Radar

 
Summary:
It would be extremely convenient to be able to define type aliases in the type parameters/constraints list.

For example, I’m implementing a polynomial algebra and I have the following definition for multiplication:

func * <Constant : Ring, Variable> (x: Term<Constant, Variable>, y: Term<Constant, Variable>) -> Term<Constant, Variable> {
	return Term(multiplication: x, y)
}

I’m having to repeat Term<Constant, Variable> quite a lot. It would be really nice to be able to define an alias:

func * <Constant : Ring, Variable, typealias Expression = Term<Constant, Variable>> (x: Expression, y: Expression) -> Expression {
	return Term(multiplication: x, y)
}

An alternative syntax would be to allow = to define an alias in a constraint:

func * <Constant : Ring, Variable, Expression where Expression = Term<Constant, Variable>> (x: Expression, y: Expression) -> Expression

Or just use ==, and make non-generic type constraints define typealiases instead of throwing errors.


Steps to Reproduce:
N/A

Expected Results:
N/A

Actual Results:
N/A

Regression:
N/A

Notes:
N/A