Show HN: Nameof Operator for Modern C++ | Hacker News Reader

Show HN: Nameof Operator for Modern C++

github.com

65 pointsneargye23 comments

This is a good use of the more modern C++ features such as string_view, constexpr and template metafunctions such as decay and enable_if.

I do wonder how much this would impact compile-times if used moderately in a large code-base.

In our project, NAMEOF_TYPE and NAMEOF almost do not add time relative to the entire project. But NAMEOF_ENUM can add a couple of seconds to large enums.

This is similar to the C preprocessor trick STRINGIZE:

  #define STRINGIZE_DETAIL(x) #x
  #define STRINGIZE(x)        STRINGIZE_DETAIL(x)

It probably uses stringification under the hood, but then relies on constexpr to "canonicalize" the name (removing everything before the dot, template parameters etc).

From cursory reading, it seems it doesn’t, at all. It uses compiler-specific predefined values __PRETTY_FUNCTION__ (gcc, clang) or __FUNCSIG__ (MS Visual C++), and doesn’t work on other compilers.

It also has to do work to extract the function name from the char arrays/C strings that those macros expand to.

Reading answers to https://stackoverflow.com/questions/4384765/whats-the-differ..., it seems it would have been easier to use the __FUNCTION__ in gcc, but I’m not familiar with that (or the other predefined values) at all, so who knows?

Actually, __FUNCTION__ won't work as it only expands to the name of the function, not any templates or arguments.

It's actually a pretty clever way to automagically deduce not only names of variables but also of enums :). Too bad it's most likely not maintainable in the long run as compilers probably change what their __PRETTY_FUNCTION__ (or equivalent) macros expand to in new versions.

I usually check the newest versions of compilers, and if the behavior changes, then I update the code

Last I knew __FUNCTION__ in GCC doesn't even do name de-mangling. You'd get the raw C symbol name with no C++ types.

https://stackoverflow.com/a/31163837/9514814

Gcc 7. I could be wrong but I seem to recall a long time ago, when I was learning this stuff in the 90s, __FUNCTION__ wouldn't even demangle.

yeap, I use __PRETTY_FUNCTION__.

You are absolutely right :)

That was what I was thinking, then I saw that this will stringify enum values, eg. nameof(c) returns "RED", which the preprocessor #x will not do.

To be sure: nameof(c) returns "c" (nameof return name of variable) nameof_enum(c) returns "RED" (nameof_enum return enum name of enum variable)

I only use STRINGIZE for error messages. I learned about it from reading the source for assert macros.

Nice work, and the header is nowhere near as complex as I had feared it would need to be.

With features C++17 this header looks not so terribly.

I wonder what including and using this does to compile times. Nothing good, I suspect.

In fact, not so much about the whole big project. May add a few seconds to the compilation.

nameof_enum doesn't work with GCC :(

Unfortunately, yes, I'm still looking for a solution for gcc

New version supported GCC >= 9

Awesome :)

Reply on news.ycombinator.com