Implicit conversion Must be used Explicitly

Question

I have a struct with the following operator declared :

public struct myStruct {
    public static implicit operator int(Nullable<myStruct> m){
        /*...*/
    }
}

This operator alone lets me implicitly convert a non-nullable struct to int, but trying to implicitly convert its nullable counterpart still raises a compilation error :

Cannot implicitly convert type myStruct? to int. An explicit conversion exists (are you missing a cast?)

Apparently the mentioned "explicit" operator is actually the implicit operator I declared, removing this operator altogether also removes the mention of the explicit one.

When it comes to nullable structs, why am I being forced to use this operator explicitly even though it was declared implicit?

EDIT:
So here is the "full code", stripped of everything that doesn't make the compiler error disappear. The struct stays literally the same, all that's new is my testing code :

using System;

public struct boilDown {
    public static implicit operator int(Nullable<boilDown> s) { return 0; }
} // END Struct

public class Sandbox {
    void Update ()
    {
        boilDown nonNullable = new boilDown ();
        Nullable<boilDown> NullableVersion = new Nullable<boilDown>();

        int MyInt;
        MyInt = nonNullable;        // this work thanks to my operator
        MyInt = NullableVersion;    // But this line requires an explicit cast
    }
}

VERSION :
You all hinted me at a c# version issue. I'm working on Unity 2017.1.0f3, which rather than .Net, uses Mono 2.0.50727.1433. (This apparently is a NET3.5 Equivalent, but even their experimental NET4.6 equivalent has this issue.)
I'll ask this question to them and see what they say.

Full code coming right up. After boiling it down to the bug, there isn't anything new to see in the struct itself, only the testing code. — Estecka
what version of C#? Console-App 4.6.1 is fine with it, no errors or warnings. — Patrick Artner

codejockie codejockie · Accepted Answer · 2017-11-19T11:20:37

You could explicitly cast the NullableVersion to int like below.

using System;

public struct boilDown {
    public static implicit operator int(Nullable<boilDown> s) { return 0; }
} // END Struct

public class Sandbox {
    static void Main()
    {

    }
    void Update ()
    {
        boilDown nonNullable = new boilDown ();
        Nullable<boilDown> NullableVersion = new Nullable<boilDown>();

        int MyInt;
        MyInt = nonNullable;        // this work thanks to my operator
        MyInt = (int)NullableVersion;    // works now
    }
}

Implicit conversion Must be used Explicitly

2 Answers