CODEWITHSUNDEEP
typescriptgenericsfactory
Moshe Gottlieb
Moshe Gottlieb

Reputation: 4003

Factory in typescript with a generic argument

I'm trying to implement a factory in typescript that returns a generic type.
Already figured out that I need to pass the type as the first argument, and setting it's type to a CTOR signature (new () => T in this example).
The problem begins when I want to pass a generic type to the factory - I get an error saying: Value of type 'typeof G' is not callable. Did you mean to include 'new'?(2348).
Is there any way to achieve this?

Here is a simplified version of the problem:

// Generic class
class G<T>{}
// Standard non generic
class B{}

function make<T>(t: new () => T){
    return new t()
}
// Works
make(B)
// Value of type 'typeof G' is not callable. Did you mean to include 'new'?(2348)
make(G<number>)

Typescript playground link to the above code.

Upvotes: 3

Views: 439

Answers (1)

johannchopin
johannchopin

Reputation: 14844

Your issue is that you set the generic in the wrong place. In make(value), value should be runnable code without any TypeScript definition. So the call make(G<number>) is false because you can't call a TypeScript generic as a parameter.

To define the generic, you need to write it before the parenthesis:

make<G<number>>(G)

So here, G<number> is the type that you give and G is the 'valid' runnable code.

Have a look at the playground.

Upvotes: 3

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