[usefulcat]

fmtlib knows the types of all the arguments, and those types are checked against the format string at compile time. So type safety ("%d" vs "%s" etc) is not really an issue.

FWIW, I have waaaay more experience with iostreams than printf. I once wrote a replacement for most parts of std::ostream purely because I had a logging system that was loosely based on log4cxx (which is based on iostreams) and I needed much faster formatting.

Right now I'm in the process of switching to a different logging system that uses fmtlib. I can say that I really, really do not miss the extreme verbosity of iostreams at all. The statefulness I could take or leave, although on balance I'd say it's usually more of a negative. Thankfully I don't have to give up type safety or extensibility.

As for treating files/strings/whatever as streams--my impression of fmtlib is that it's concerned primarily with formatting, which frankly I'm fine with. It can write to an in-memory buffer or to a FILE* or to a std::ostream, which covers pretty much all of my needs. Given the performance of iostreams (lots of virtual method calls) I never really saw the point of using it as a more generalized 'streaming' interface, even knowing that it's possible.