CODEWITHSUNDEEP
typescript
FindOutIslamNow
FindOutIslamNow

Reputation: 1236

TypeScript interface with generic multiple call signatures

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"));

Upvotes: 1

Views: 1601

Answers (1)

Titian Cernicova-Dragomir
Titian Cernicova-Dragomir

Reputation: 249636

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"));

Upvotes: 4

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