Swift - store values in map. Different behaviour in structs vs classes

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This example Swift code does not compile if SomeClass is defined as struct. The compiler says: @value $T6 is not identical to (String, Proto)

However, the compiler does not complain if SomeClass is a class.

Why?

public protocol Proto {
    func hello(value:Int)
}


public struct SomeClass {

    var map = [String:Proto]()

    public func store (key:String, value:Proto) {

        map[key] = value // That does not work if SomeClass is a struct  

    }
}

asked 20 secs ago

abnormi

16

Swift - store values in map. Different behaviour in structs vs classes