Consider contextually typing class member functions by their base class/interface members

[kns98]

here is my code

 export enum SortDir
 {
 Asc,
 Desc,
 Flip
 }

 export interface ISortInfo
 {
 getvalue(x: QuerySummary): any; //change to number|string in TypeScript 1.4
 order: SortDir;
 ordercalc?: number;
 }

 class SortByQueryId implements ISortInfo
 {
 getvalue = x => x.QueryId;
 order = SortDir.Flip;
 }

when I type "x." I expect to see the properties of QuerySummary but I do not. VS still thinks the type is 'any'

[danquirk]

Contextual typing has only ever been applied to expressions and not statements so this has never worked. That said, it's certainly a reasonable thing to expect, at least for the function declaration style:

class SortByQueryId implements ISortInfo {
 getvalue(x) { /* x should be QuerySummary in here */ }
}

Edited the title slightly to reflect this.

[kns98]

Thanks Dan. I love this open community style development process :)

[jbrantly]

Can the scope of this be expanded to support member properties and static properties? See my comment in #1887 for an example.

[hdachev]

Adding an example of broken return value inference that results in a compiler error:

type Events = {
 [event: string]: () => void;
};

class A {
 getEvents(): Events {
 return null;
 }
}

class B extends A {
 getEvents() {
 return {
 'click': () => {

 }
 };
 }
}

// test.ts(12,7): error TS2415: Class 'B' incorrectly extends base class 'A'.
// Types of property 'getEvents' are incompatible.
// Type '() => { 'click': () => void; }' is not assignable to type '() => { [event: string]: () => void; }'.
// Type '{ 'click': () => void; }' is not assignable to type '{ [event: string]: () => void; }'.
// Index signature is missing in type '{ 'click': () => void; }'.

[omidkrad]

+1 vote for this. Related issues: #178 and #2073

I think it's not intuitive for contextual typing not to apply when overriding a class member. i.e. it should.

[j-walker23]

+1