RFC #24: Struct inheritance

[ProCode-Software]

• In Klar, we want inheritance to be solely based on copying fields and methods, rather than full OOP. There will not be a super() constructor that must be called. The first idea that comes to mind is copying fields from other types, and if there is a field collision between 2 inherited types, it must be explicitly overriden.

type A { x: Int }
func A.hasX() = self.x != 0

type B { x: String }
func B.hasX() = self.x != ""

type MyStruct: A, B {
    // Since there is a collision between field 'x', it must be explictly declared here
    x: Float
}

There are a few concerns with this:

1. In the declaration, it says type MyStruct inherits A and B, but when we override a field's type, MyStruct cannot be converted to either type. This is misleading.
2. There will be no method hasX on MyStruct because the methods on both inherited types reference the field x of a different type. With these rules, it may not be clear what methods MyStruct inherits (finding out may require looking in the bodies of several methods in the inherited types, which may also have their own inherited types).
3. In structs, field declarations can refer to other fields, such as type X { x: Int, y: Int = self.x }. A type override could remove other fields.

I would like some ideas on how inheritance can be implemented, such as Go-style embedding.