swift – 使用或不使用’where’子句与泛型有什么区别？

func foo<T: SomeClass>(object: T) -> Array<T>

func foo<T>(object: T) -> Array<T> where T: SomeClass

The requirements in a generic where clause specify that a type
parameter inherits from a class or conforms to a protocol or protocol
composition. Although the generic where clause provides syntactic
sugar for expressing simple constraints on type parameters (for
instance, <T: Comparable> is equivalent to <T> where T: Comparable and
so on), you can use it to provide more complex constraints on type
parameters and their associated types. For instance, you can constrain
the associated types of type parameters to conform to protocols. For
example, <S: Sequence> where S.Iterator.Element: Equatable specifies
that S conforms to the Sequence protocol and that the associated type
S.Iterator.Element conforms to the Equatable protocol. This constraint
ensures that each element of the sequence is equatable.

简单地说,在其中允许您指定关于通用参数的关联类型的约束,而在<>中你不能这样做.