Can We Create a \'Static Warning\' Like `static_assert` but with Warnings Instead of Errors?

Is There a "Static Warning"?

This question delves into the possibility of implementing a "static_warning" construct that functions akin to static_assert but generates only a warning during compilation rather than an error that immediately halts compilation. Let's dive into the exploration and answer the question.

A Static Warning Analogue

Inspired by a comment from Michael E, a compelling solution involves modifying macros to meet the desired functionality:

<code class="c++">#define STATIC_WARNING(cond, msg) struct PP_CAT(static_warning,__LINE__) { \
  DEPRECATE(void _(const ::detail::false_type&),msg) {}; \
  void _(const ::detail::true_type& ) {}; \
  PP_CAT(static_warning,__LINE__)() {_(::detail::converter<(cond)>());} \
}</code>

This code employs the DEPRECATE macro to flag specific methods as deprecated, conveying warnings at certain points in the program flow.

Example usage of the STATIC_WARNING macro:

<code class="c++">STATIC_WARNING(1 == 2, "Failed with 1 and 2");</code>

Results

When compiling with the appropriate warning level, the compiler will issue a warning message that resembles the intended behavior: "'_' is deprecated:... ."

This allows for run-time information and debugging assistance without prematurely terminating compilation. However, it's important to note that the behavior of macros is compiler-specific, and different compilers might handle them differently.

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