Refactor Converter Class to use C++17's if constexpr or Type Traits Instead of RTTI

[T1t4m1un]

Hello rapidcsv maintainers,

Firstly, thank you for your hard work on this library. I was going through the Converter class and noticed that RTTI (typeid()) is used to determine the type for static conversion. While this approach works, using RTTI can increase the binary size and is generally discouraged unless truly necessary.

Instead, I suggest refactoring this piece of code to leverage C++17's if constexpr for compile-time checks or using type traits. This would ensure that only the necessary branch of code is compiled for a particular type, resulting in more optimized binary code.

Here's an example of what it might look like using if constexpr:

template<typename T>
void ToVal(const std::string& pStr, T& pVal) const
{
    try
    {
        if constexpr (std::is_same_v<T, int>)
        {
            pVal = static_cast<T>(std::stoi(pStr));
        }
        else if constexpr (std::is_same_v<T, long>)
        {
            pVal = static_cast<T>(std::stol(pStr));
        }
        // ... continue for other types
    }
    catch (...)
    {
        // ... error handling
    }
    // ... remaining code
}

Or considering to support lower version C++, SFINAE techniques can be used to replace if constexpr statement like this:

template<typename T>
class Converter
{
public:
    template<typename U = T, std::enable_if_t<std::is_same<U, int>::value, int> = 0>
    void ToVal(const std::string& pStr, T& pVal) const
    {
        pVal = static_cast<T>(std::stoi(pStr));
    }

    template<typename U = T, std::enable_if_t<std::is_same<U, long>::value, int> = 0>
    void ToVal(const std::string& pStr, T& pVal) const
    {
        pVal = static_cast<T>(std::stol(pStr));
    }

    // ... Continue for other types ...

    // ... Remaining code ...

    // Default case, if no other type matches.
    void ToVal(const std::string& pStr, T& pVal) const
    {
        throw no_converter();
    }
};

[d99kris]

Hi @T1t4m1un - I agree typeid() if-else-chain is much less than ideal. In an initial implementation (before publishing on github) I believe I used templating for ToVal / ToStr, but ended up with current design to allow for more flexibility when overriding.

Btw, another related suggestion came up in #134.

I'm willing to consider a PR that maintains C++11 support as well as backward-compatibility. But if it falls outside of that, I think it may be better to fork and create a new project. I don't want rapidcsv to diverge from it's current functionality / supported platforms too much.

[d99kris]

I will proceed to close this issue for now, as I do have plans to address it. But again as mentioned, a PR would be considered if it fulfills the stated requirements.