I really like your code style.

It's not so important, but anyway, in next free function:

std::string concat(const std::vector<std::string>& strings, const std::string& delim = "")

Maybe you wanted the delim default value to be " " space? or not?

I really like your code style.

It's not so important, but anyway, in next free function:

std::string concat(const std::vector<std::string>& strings, const std::string& delim = "")

Maybe you wanted the delim default value to be " " (a space)? or not?

I really like your code style.

It's not so important, but anyway, in next free function:

std::string concat(const std::vector<std::string>& strings, const std::string& delim = "")

maybe you wanted mean that the delim default value is " " space? or not?

thanks!

I really like your code style.

It's not so important, but anyway, in next free function:

std::string concat(const std::vector<std::string>& strings, const std::string& delim = "")

Maybe you wanted the delim default value to be " " space? or not?