Make implicit this part of function signature.

[Akhristenko]

Search Terms

implicit this method signature

Suggestion

Include implicit this in method signature when this used in method body and we can infer this type.

Use Cases

This help us find cases when we pass method of object as callback without using bind.

Examles

Let we have current class, function and class instance:

class Test {
    str = "string";
    impl() {
        return this.str;
    }
    expl(this: Test) {
        return this.str;
    }
}

function test(cb: (this: void) => string) {
    alert(cb());
}

let obj = new Test();

If we write test(obj.expl) we get compilation error.
In this code this inside impl() function infer to Test type
but if we write test(obj.impl) we don't get compilation error and get runtime error.

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

[ahejlsberg]

Duplicate of #7968.