If you use a general meta layer preprocessor such as MyDef, you may be able to construct macros that comes from evaluations of code in any languages (instead of restricted in eg. C++ with rather complicated compiler mechanics)
A constexpr is a constant that is evaluated from a code at compile time, which is essentially just macros. Right?
A general preprocessor that just do language agnostic code manipulations are not difficult but rather useful. Much complicated syntax sugar I see in the recent language development become unnecessary if a general preprocessor is in place (where syntactic sugar belong). I wonder why it is often not used.
> A constexpr is a constant that is evaluated from a code at compile time, [...]
It's rather a constant expression, which is quite a bit more than a mere constant.
> [...] which is essentially just macros. Right?
Macros are basically just text replacement. You can't write a macro and expect most compilers to execute the expressions and code inside the macro at compile-time. Some compilers may still to do that, but it's not very common for more complicated stuff. With constexpr you get a guarantee that the expression can be evaluated at compile-time and it gives quite a good hint to the optimizer to spend more time optimizing that portion of the code.
With a macro, you get guarantee of compile time evaluation, as well as compile time independent literal syntax double check. And you can do better than hint. You can double check the results explicitly. Since it's compile time evaluation, optimization is out of context.
I didn't find any, so I rolled my own 10 years ago. Most of its features are suited toward very limited users. E.g. it doesn't really support macro evaluation from arbitrary language, only from Perl currently (but general for any target language). However,to support macro evaluation from arbitrary language seems trivial. It'll be just like gcc pulling different compiler together.
A constexpr is a constant that is evaluated from a code at compile time, which is essentially just macros. Right?
A general preprocessor that just do language agnostic code manipulations are not difficult but rather useful. Much complicated syntax sugar I see in the recent language development become unnecessary if a general preprocessor is in place (where syntactic sugar belong). I wonder why it is often not used.