Definition of fail_fast and of narrowing_error triggers clang's -Wweak-vtables

[mrahn]

As fail_fast and narrowing_error are deriving from std::logic_error and from std::exception respectively, they both have a vtable. In a header-only library there is no compilation unit, which implies the vtables are emitted in every client compilation unit, putting burden to the linker to understand this is not a duplicate definition. That is what the warning is about.

Solution

• Disable the warning locally.

Alternatives:

• introduce a compilation unit (NO because: header-only is wanted)
• do not use a custom exception (NO because: https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#e14-use-purpose-designed-user-defined-types-as-exceptions-not-built-in-types)
• introduce template<typename = void> fail_fast ... and throw fail_fast<> (NO because: Introduces complexity to hide a warning is never a good idea.)
• disable all warnings (NO because: 1. Unclear how that would even work if header is copied by clients. 2. Warnings are friends.)

References:

• See https://github.com/mrahn/test_gsl_lite_weak_vtables for a reproducer (which is basically: include the header with -Wweak-vtables on)
• See add SYSTEM to target_include_directories #321 for a workaround that disables all warnings for the gsl-lite header

[mbeutel]

Thanks for the diligent bug report :) I will address this problem as soon as time allows.

[mbeutel]

This should now be fixed. I'm sorry it took so long.