TypeScript: get type of instance method of class

You could use TypeScript's built in InstanceType for that:

class MyClass
{
  private delegate: InstanceType<typeof MyClass>['myMethod']; // gets the type (boolean) => number;

  public myMethod( arg: boolean )
  {
    return 3.14;
  }
}

you can use the following type:

type TypeOfClassMethod<T, M extends keyof T> = T[M] extends Function ? T[M] : never;

With that, you can write the following:

class MyClass
{
  private delegate: TypeOfClassMethod<MyClass, 'myMethod'>; // gets the type (boolean) => number;

  public myMethod( arg: boolean )
  {
    return 3.14;
  }
}