I am working on an instantiator function that generates an instance of a provided class:
declare type ClassType = { new (): any }; // known as "ParameterlessConstructor"
function createInstance(constructor: ClassType): any {
return new constructor();
}
Is there a way for me to modify the function so that it produces an instance of the specified constructor, rather than just returning any? I want to ensure type safety for users of this function.
It turned out to be surprisingly simple; all I had to do was work around the limitations imposed by my own code.
The secret lies in defining the constructor parameter as a type that can create a new instance of a generic type. This generic type, T, must match the generic type returned by the getInstance function:
function getInstance<T>(constructor: { new (): T }): T {
return new constructor();
}
By following this approach, the expected outcomes can be achieved:
class Foo {
public fooProp: string;
}
class Bar {
public barProp: string;
}
var foo: Foo = getInstance(Foo); // No issues
var bar: Foo = getInstance(Bar); // Error: Type 'Bar' is not compatible with type 'Foo'
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