CODEWITHSUNDEEP
typescriptgenericstype-inferencetypescript-generics
user4704976
user4704976

Reputation:

Generic TypeScript function that instantiates classes

I set out to write a generic TypeScript function that takes a class constructor as an argument, as well as any arguments required by the constructor, and returns a new instance of the class. One of my requirements is that the return type and constructor argument types must be inferred by the compiler.

After some trial and error I came up with a working version that seems to do what I need (see below). But, is there a better way to achieve this?

function instantiate<Params extends any[], Instance>(
    ctor: new (...args: Params) => Instance, ...args: Params
) {
    return new ctor(...args);
}

Example usage:

class Circle {
    constructor(public radius: number) {}
}

class Rectangle {
    constructor(public width: number, public height: number) {}
}

const circle = instantiate(Circle, 5);
const rectangle = instantiate(Rectangle, 3, 7);

Try on TypeScript Playground

Upvotes: 5

Views: 444

Answers (1)

smac89
smac89

Reputation: 43098

You can make it simpler in terms of your use of generic types by making use of the ConstructorParameters and InstanceType utility types:

function instantiate<T extends new (...args: any[]) => any>(
    ctor: T, ...args: ConstructorParameters<T>
): InstanceType<T> {
    return new ctor(...args);
}

Upvotes: 4

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