Assertions in header files slows down an interpreter, so they should be
turned off by default (simple `make`). To enable them, define a macro
`RUBY_DEBUG=1` (e.g. `make cppflags=-DRUBY_DEBUG` or use `#define` at
the very beggining of the file. Note that even if `NDEBUG=1` is defined,
`RUBY_DEBUG=1` enables all assertions.
[Feature #16837]
related: https://github.com/ruby/ruby/pull/3120
`assert()` lines in MRI *.c is not disabled even if `RUBY_DEBUG=0` and
it can be disabled with `NDEBUG=1`. So please consider to use
`RUBY_ASSERT()` if you want to disable them when `RUBY_DEBUG=0`.
https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html says:
> GCC never returns 1 when you call the inline function with a string
> constant or ...
Because rb_str_new and familiy take string constants, it was a bad idea
for them to contain RB_CONSTANT_P. We should instead do so in
corresponding macros. [ruby-core:98212]
