关于类型的Swift通用约束

Question

Is it possible to define a class whose generic parameters both conform to some given type?

For example

protocol Foo{}
class Bar : Foo {}
class Baz : Foo {}
class Qux<T, U, V where U: T, V: T> {}

let qux = Qux<Foo, Bar, Baz>()

Answer 1

No. Not to a type. Type constraints specify that a type parameter must inherit from a class, or conform to a protocol or protocol composition:

class SomeClass<TypeParameter: ProtocolOrClass>

Why don't you just do:

protocol Foo {}
class Bar: Foo {}
class Baz: Foo {}
class Qux<U: Foo, V: Foo> {}

let qux = Qux<Bar, Baz>()