SwiftGenericTypesAsFactoryParameters.swift

// Say you have a generic class with a couple of generic types, 
// that also takes a couple of parameters in its initializer:

class Foo<T, U, V> {
  init(label: String, other: Any) {
    // ...
  }
}

// Instantiating objects of this class in the standard way, while not unusual,
// can make for some ugly init code. The fact that the generic types aren't 
// labeled make it unclear which types are required in which positions. 
// There's also no nice way to format the types on separate lines.

let foo1 = Foo<MyClass1, MyOtherClass2, SomeExampleResultHandler>(label: "foo1", other: MyClass3.shared)

// We can make initializing much nicer with a factory:

class FooFactory {
  func createFoo<T, U, V>(
    inputType: T.Type, 
    outputType: U.Type, 
    resultHandlerType: V.Type, 
    label: String, 
    other: Any) -> Foo<T, U, V> {
    return Foo<T, U, V>(label: label, other: other)
  }
}

// ... which can then be used like this:

let foo2 = FooFactory.createFoo(
  inputType: MyClass1.self,
  outputType: MyOtherClass2.self,
  resultHandlerType: SomeExampleResultHandler.self,
  label: "foo2",
  other: MyClass3.shared)

// The generic types have been from of the `<...>` part of the declaration,
// which is unlabeled and difficult to format,
// and to parameters for the factory method.