Nominal classes

[kaleidawave]

126 adds allowing creating classes as a type which can be referenced

As of #126 they are treated as being nominal. Given

class X { a: number = 2 }

The only two cases of types where instance passes is for

const x: X = instance

is when

• Type::Constant has a base type (there is a function in the code which does this) that is X. (this is because string, number and boolean are treated as special classes)
• Type::Object where the information.prototype.get(object_type_id) is X

Therefore it does not perform property checks for let x: X = { a: 2 } and so will raise a type error. However it only works one way, so let x: { a: number } = new X is fine.

There is also some benefit to the variable_current_value and side effect system which means that shouldn't create to many issues. For let x: { a: number } = new X, x still has the class instance of X type as it doesn't widen.

This can simplify things. In the future:

• The methods on X can be treated as a known function and therefore know the side effects (if they are already registered)

However TypeScript allows both ways. There may be a way in the future for a CLI flag to check properties (and also drop that for (x: Set<number>) => x.add x.add might not be the Set.prototype.add function)