Broken Value Type Wrapping

broken_value_type_wrapping.cs

// This is broken in Unity 5.x's built-in version of Mono, which is admittedly rather old.
// Compiling with VS2013 it works as intended.

public struct WrapperType<T> {
    public float Timestamp;
    public T Value;
}

public struct MyValueType {
    public float floatA;
    public float floatB;

    public static void Test() {
        var valInst = new MyValueType() {
            floatA = 1234f,
            floatB = 5678f
        };

        var wrappedValInst = new WrapperType<MyValueType>() {
            Timestamp = 0.135f,
        };
        wrappedValInst.Value = valInst;

        Debug.Log("try 1: " + wrappedValInst.Value.floatA + ", " + wrappedValInst.Value.floatB);

        var identityWrappedValInst = Identity(wrappedValInst.Value);

        Debug.Log("try 2: " + identityWrappedValInst.floatA + ", " + identityWrappedValInst.floatB);

        // try 1: 1234, 5678
        // try 2: 0.135, 1234
        // Values have shifted to include WrapperType.Timestamp, what the...
        // So where does the value of floatB end up?
    }

    public static MyValueType Identity(MyValueType a) {
        return a;
    }
}