FunctionBuilder.ts

type ParamBuilder<TArgs extends Record<string, any>, TReturn> = {
  [K in keyof TArgs]: (arg: TArgs[K]) => ParamBuilder<Omit<TArgs, K>, TReturn>;
} & (keyof TArgs extends never ? { call(): TReturn } : {})

function builderFor<TArgs extends object, TReturn>(fn: (args: TArgs) => TReturn) {

  const args: TArgs = {} as unknown as TArgs;
  return new Proxy({}, {
    get(self, prop) {
      if (prop === "call") {
        return () => fn(args);
      }

      return (value: any) => {
        args[prop] = value

        return this;
      }
    }
  }) as unknown as ParamBuilder<TArgs, TReturn>;
}

function testFn(args: { color: "red" | "blue", size: "large" | "medium" }) {

  return args.color;
}

const builder = builderFor(testFn)
  .color("red")
  .size("large")

TS 🧙 @Beng89 thank you for this bit of gold 😲 💯 🥇