Design Meeting Notes, 4/21/2017

[DanielRosenwasser]

Check non-optional properties initialized in constructor (#8476)

• Why are we revisiting?
  • The --strict flag makes it easier to surface these highly specific checks.
• Ideas
  • Ensure that values are initialized at every point of exit in the constructor body.
  • But this doesn't completely guarantee coverage for checks because of super() calls and virtual methods.
    • i.e. what if methods override and don't initialize appropriately?
• But there's definitiely people bitten by this.
• Not clear that this is the desirable behavior in --strict.
  • --strict is what we believe to be the the set of ideal settings for writing new code.
  • What makes this more desirable that --noImplicitReturns?
    • That was a toss-up as well.
• What about Angular and the like? They wouldn't be able to use this flag.
  • Angular codebases (especially ones made by angular-cli) and the like should be explicit about their strictnesss options.
  • Or they could explicitly turn it off when upgrading projects.
• Resolution: Let's do it, experiment

String enums (#3192)

• Today, emulating string enums can be done with the following hack:

namespace Color {
    export const None = undefined;
    export type  None = undefined;

    export const Red: "red" = "red";
    export type  Red = typeof Red;

    export const Green: "green" = "green";
    export type  Green = typeof Green;

    export const Blue: "blue" = "blue";
    export type  Blue = typeof Blue;
}

type Color = Color.None | Color.Red | ...;

• Questions & ideas

  • Syntax
    • Would be great not to need another modifier on enums.
  • Should we produce a new type for each enum member?

• Idea

  1. Enum with non-literal members.
  2. Enum with only numeric literal members.
  3. Enum with only literal members, some of which are non-numeric.

• Should each enum member widen?

  • Do they widen to string or to their base enum type?
  • Most people agree base enum type.

• Reverse indexing?

  • Probably wouldn't be able to do that?

• Question:

  • What happens when you have Color.Red | Alert.Red and they refer to the same literal type?

Out of time.