swift不透明类型的整型不能赋值给整型？

Question

func A() -> some Equatable {
    1
}

print(type(of: A()))


var x: Int = 0
x = A()

Answer 1

Swift不透明类型的整型不能直接赋值给整型。因为类型不匹配，A() 返回 Some Equatable, 所以把A()赋值给x时候需要进行类型转换

func A() -> some Equatable {
    1 
}

print(type(of: A()))   //Output  is Int

var x: Int = 0
//error: cannot assign value of type 'some Equatable' to type 'Int'
//类型不匹配所以需要添加 as！Int 进行转换

x = A() as! Int

print(x) //Output is 1

Refs

https://docs.swift.org/swift-book/LanguageGuide/OpaqueTypes.html
swift 的协议以及不透明类型