Design Meeting Notes, 11/11/2016

[DanielRosenwasser]

Design Meeting 11/10/2016

readonly and literal types

• Intentional breaking change or a bug: Readonly vs. litteral type breaking change? #12148

• Resolution: first case doesn't make much sense, second case is a bug.

Mapped types (#12114)

• Related issues:

  • Spread and Rest and Object.assign
  • Optional
  • String literal types as index signature parameter types?, Index signature parameter type should allow for enums and 'rest' index signatures
  • Allow classes to be parametric in other parametric classes
  • Allow class to extend from a generic type parameter

• Release schedule

  • 2.1 or not

• Iterates over a union of literal types and generates properties of some type for given literal names.

• Effectively a macro for types.

• AO: Only problem is that this could make your language service could never return.

  • AH: No, we cut off after a certain recursion depth, otherwise this could never work.

• AH: It may be the case that type aliases and interfaces shouldn't be nearly as distinct as they currently are.

  let x: T & U;

  • & in some sense is not hugely different from the operation that classes extend other classes.
    • How do you do error reporting in this system?
      • Still not clear.
      • Classes can still do extra checks - but it's not like that should stop this feature.

• Resolution: Let's pull it in, get some feedback on it for the next 2 weeks.