Question

Background

I have some generic code for persistence that uses boost::variant to store multiple types. While outputting values, I had to write a converter function protected_backslash_n, which does nothing, in the default case, but return the same value back.

In the specialised case where the template parameter is a std::string I use boost::regex_replace() to search for \n and replace it with \\n.

Question

The code works fine, but it would be nice if I could get rid of the extra copy in the generic case, due to the return-by-value.

Is there a way to do this while allowing the specialised std::string version to work fine?

I tried changing the return value to T const&, but then the specialised version won’t match up.

Error

GetPipedValues.hpp:15:21: error: template-id ‘protect_backslash_n<std::string>’ for ‘std::string pitbull::protect_backslash_n(const string&)’ does not match any template declaration

Code

template<typename T>
inline T protect_backslash_n( T const& orig )
{
    return orig;  // BAD: extra copy - how do I get rid of this?
}

template<>
inline std::string protect_backslash_n<std::string>( std::string const& orig )
{
    boost::regex expr("(\\n)");
    std::string  fmt("(\\\\n)");
    return boost::regex_replace(
        orig, expr, fmt, boost::match_default | boost::format_all
    );
}

Answer 1

Don’t make it a template, but just an overload. The compiler will choose that function over a template instantiation, if the parameter matches.

std::string protect_backslash_n( std::string const& orig);