TypeScript interface with generic multiple call signatures

Question

I want to have multiple call signatures in an interface, such that they have different generic arguments

interface GenericIdentityFn {
    <T>(arg: T): T;
    <T, F>(arg1: T, arg2: F): [T, F];
}

function identity<T>(arg: T): T {
    return arg;
}

// error: duplicate definition
function identity<T, F>(arg1: T, arg2: F): [T, F] {
    return [arg1, arg2];
}

let myIdentity: GenericIdentityFn = identity;

console.log(myIdentity("hello"));

Titian Cernicova-Dragomir · Accepted Answer · 2018-08-09 12:18:04Z

4

You can't have multiple implementations of a function. You can have a function with multiple signatures, but one implementation and it is up to you in the implementation to discern the signature that was called.

If you define the function with multiple overloads you will be able to assign it to the GenericIdentityFn interface

interface GenericIdentityFn {
    <T>(arg: T): T;
    <T, F>(arg1: T, arg2: F): [T, F];
}

function identity<T>(arg: T): T;
function identity<T, F>(arg1: T, arg2: F): [T, F]
function identity<T, F>(arg1: T, arg2?: F): T | [T, F] {
    return typeof arg2 === 'undefined' ? arg1 : [arg1, arg2];
}

let myIdentity: GenericIdentityFn = identity;

console.log(myIdentity("hello"));

answered Aug 9, 2018 at 12:18

Titian Cernicova-Dragomir

253k37 gold badges465 silver badges395 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

TypeScript interface with generic multiple call signatures

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related