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extension methods
Suggestion, part 1
With the risk of you stopping to read here, this is related to extension methods: #9. I actually wrote a post on this #35280, but I guess notifications are turned off when the issue is closed, so with the risk of being perceived as slightly spammy I post again.
@RyanCavanaugh and @hax: Extension methods already exists! Eh...what? Well, I thought I'd write a language service plugin (see #35280), only to realize, they actually work well enough for me already, with symbols and classic Javascript prototype extensions. The idea is to just extend e.g. Date with a isLeapYear (or Object with IFooExtensionMethod) and add the right typings. See https://github.com/staeke/ts-extension-methods. This requires typescript@next since some bug for auto-complete suggestions was recently fixed. Please tell me if there's something I've missed!
So suggestion 1 - promote this style. No actual language change.
Suggestion, part 2
In terms of syntax, this works and is terse on the consumer side, but maybe a little verbose on the provider side (less of a problem though). If you wanted to fix that here are some thoughts:
// First simplify extending types in general, by skipping the declare module syntax.
// Rather reuse "extends" (symbol after is non-ambiguous, auto-import works.)
// Also you can choose whether it's just typings (abstract, no implementation)
// or an expected prototype override (implementation) which will add to prototype
extends Date {
someMethod(); // Just typing
isLeapYear(this: Date) { .. } // Will extend Date.prototype
}
// Now we want symbols, and a way to export those so we allow that inline
extends Date {
[export symbol isLeapYear]: function(this: Date) {...}
}
// For interfaces
extends Object {
[export symbol bar]: function(this: IFoo) { ... }
}This would be equivalent to
export const isLeapYear = Symbol()
function isLeapYearImpl(this: Date) { .. }
declare global {
export interface Date {
[isLeapYear]: typeof isLeapYearImpl;
}
}
Date.prototype[isLeapYear] = isLeapYearImpl;Examples
Checklist
Suggestion 1 (nothing) obviously meet all criterias. Suggestion 2:
- [ x ] This wouldn't be a breaking change in existing TypeScript/JavaScript code
- [ x ] This wouldn't change the runtime behavior of existing JavaScript code
- [ x ] This could be implemented without emitting different JS based on the types of the expressions
- [ x ] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
- [ x ] This feature would agree with the rest of TypeScript's Design Goals.