We have the following c++ code using catch2 framework:
auto check2 = [](size_t exp, size_t val, auto comp) {
REQUIRE(comp(exp, val));
};
check2(10, 20, std::equal_to<size_t>{});
and clang-tidy generates the following
/test_lingua.cpp:1236:36: warning: prefer transparent functors 'equal_to<>' [modernize-use-transparent-functors]
check2(10, 20, std::equal_to<size_t>{});
^
Can any (reasonable) change to the code make clang-tidy happy?
UPDATE:
The original code compared size_t
and nlohmann::json
(something like REQUIRE(comp(val, exp_dict[s]));
) and the problem using std::equal_to<>{}
resulted in this compilation error
1>test_lingua.cpp(1224,25): error C2672: 'operator __surrogate_func': no matching overloaded function found
1>test_lingua.cpp(1227): message : see reference to function template instantiation 'void maz::tests::test_superscript_remover::<lambda_afa1c9ba8dd5ae9bea1ac934f5f796ab>::()::<lambda_9d6a94e643f0b9fe3677202d1edfa8f2>::operator ()<std::equal_to<void>>(const std::string &,size_t,std::equal_to<void>) const' being compiled
1>test_lingua.cpp(1224,1): error C2893:
Failed to specialize function template 'unknown-type std::equal_to<void>::operator ()(_Ty1 &&,_Ty2 &&) noexcept(<expr>) const'
1>E:\VS019\VC\Tools\MSVC\14.29.30037\include\xstddef(198): message : see declaration of 'std::equal_to<void>::operator ()'
In order to fix this, you had to also use .get<size_t>()
in order for the perfect forwarding to work.
You simply replace
std::equal_to<size_t>{}
with
std::equal_to<>{}
(C++14 and above, uses template default argument) or
std::equal_to{}
(C++17 and above, uses CTAD).
This way the std::equal_to<void>
specialization is used, which generically compares two arguments a
and b
of any types as if by a == b
(plus perfect forwarding).
It avoids having to specify the correct types again, so you don't have to repeat yourself, which may sometimes be a source of error (e.g. if the types are changed but the std::equal_to
template argument is not correctly updated).