Using Class Types in Generics

When creating factories in TypeScript using generics, it is necessary to refer to class types by their constructor functions. For example,

function create<T>(c: {new(): T; }): T {
  return new c();
}

A more advanced example uses the prototype property to infer and constrain relationships between the constructor function and the instance side of class types.

class BeeKeeper {
  hasMask: boolean;
}
 
class ZooKeeper {
  nametag: string;
}
 
class Animal {
  numLegs: number;
}
 
class Bee extends Animal {
  keeper: BeeKeeper;
}
 
class Lion extends Animal {
  keeper: ZooKeeper;
}
 
function findKeeper<A extends Animal, K> (a: {new(): A;
  prototype: {keeper: K}}): K {
 
  return a.prototype.keeper;
}
 
findKeeper(Lion).nametag;  // typechecks!

Links:

https://www.typescriptlang.org/docs/handbook/generics.html#using-class-types-in-generics

doc_TypeScript

2025-01-10 15:47:30

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