Question

Based on this question:

"enum class" emulation or solid alternative for MSVC 10.0

I would like to ask a couple of things. Assuming this code:

struct DeletionMode_E
{
    static DeletionMode_E const Off;
    static DeletionMode_E const DirSize;
    static DeletionMode_E const FileNumberSize;
    static DeletionMode_E const DirAndFileNumberSize;

    operator int const() const { return myVal; }

private:
    explicit DeletionMode_E(const int & v) : myVal(v) { }
    const int myVal;
};

And their subsequent definitions :

    Log4Reconstruction::DeletionMode_E const Log4Reconstruction::DeletionMode_E::Off(0);
    Log4Reconstruction::DeletionMode_E const Log4Reconstruction::DeletionMode_E::DirSize(1);
    Log4Reconstruction::DeletionMode_E const Log4Reconstruction::DeletionMode_E::FileNumberSize(2);
    Log4Reconstruction::DeletionMode_E const Log4Reconstruction::DeletionMode_E::DirAndFileNumberSize(3);

One can use this like :

    void Log4Reconstruction::setDeletionMode( Log4Reconstruction::DeletionMode_E const & delMode_in)
    {
        std::cout << delMode_in << std::endl;

        switch(delMode_in)
        {
        //case Log4Reconstruction::DeletionMode_E::Off: C2051 case expression not constant
        //  std::cout << "Off" << std::endl;
        //  break;
        case 1:
            std::cout << "File number" << std::endl;
            break;
        }
    }

Why is the function call operator called? How would one call it manually in order to solve the “problem” in the case statement? I am using MSVS 2008 no external libs are available.

Answer 1

There is no function-call operator declared here.

operator int const() const { return myVal; }

Is a user-defined conversion which converts an object of type DeletionMode_E to a constant integer. To invoke it, you have to perform a cast (this is done implicitly in your switch-statement).