Suggestion for readonly interface

Avoid duplicating “readonly” for each property by applying it to the interface definition itself. This is to reduce boilerplate code defining immutable objects.

Having interface where ALL properties are read only:

interface State {
    readonly prop1: string;
    readonly prop2: string;
    ...
    readonly prop22: string;
}

equals to:

readonly interface State {
    prop1: string;
    prop2: string;
    ...
    prop22: string;
}

[RomainMuller]

I think there might be value in extending this to cover a C++ like const behavior…

const interface Foo {
  property: string; // Implicitly readonly
  method(): void; // Cannot mutate `this`
}

interface Bar {
  const method(): void; // Guaranteed non-mutating
  mutatingMethod(): void; // Could mutate `this`
}

function baz(obj: const Bar) { // Require "obj" to not be mutated by implementation
  obj.mutatingMethod(); // 💥 illegal call of mutating method on const reference
}

I don’t have particularly strong feelings on the const versus readonly term here… const is “nice” to me as it relates nicely to what this means in C++, which (some) people are used to.

[aleclarson]

const interface might be nice for deep readonly (kinda like { a: { b: 1 } } as const)