if应不应该为constexpr和它的上层或下层if是不是constexpr没有关系,应不应该为constexpr只由你的程序...
很明显,代码的可读性就有些被破坏了。来到C++17后,就可以使用if-constexpr了: template<typenameT>std::stringtoStr(Tt){ifconstexpr(std::is_same_v<T,std::string>)returnt;elsereturnstd::to_string(t);} 代码的可读性与上面使用enable_if相比好了许多! 本文主要参考了下面两篇文章:...
If there's an if-constexpr, how come there's no switch-constexpr? if constexpr was ultimately derived from a more sane form of the static if concept. Because of that derivation, applying the same idea to switch does not appear to have been considered by the ... ...
Alternatively, we can also put the name of the concept instead of atypenameand without therequiresclause: template<std::is_floating_pointT>constexprboolclose_enough20(Ta,Tb){returnabsolute(a-b)<precision_threshold<T)>;} In this case, we also switched fromis_floating_point_vinto a conceptfloat...
template<typenameT>autoGetValue(Tt){ifconstexpr(sizeof(int)==4){return"hello";}else{return1;}} 通过比较可以得出,运行时的if语句可以将else省略放到外面,但是编译期的if语句不能这么使用,因为这可能导致函数返回两个不同的类型返回值从而导致编译失败。
Basically - the lambda gives you a place where you can if constexpr on that constraint. But the lambda can't return a type, it can only return a value - so we instead return some kind of std::type_identity<T>. And then we need to decltype(...)::type to actually pull the...
; template < class... TTypes > class C { private: template<typename TToMatch> static constexpr bool c_fVariantTypesContain = OneOfTheseTypes<TToMatch, TTypes...>; public: void F() const noexcept requires(c_fVariantTypesContain<int> || c_f...
if constexpr (std::is_base_of_v<std::random_access_iterator_tag, typename std::iterator_traits<Iterator>::iterator_category>) return detail::makeBinaryBlockFast(type, first, last); else return detail::makeBinaryBlockSlow(type, first, last); } /** 128 changes: 48 additions & 80 deletion...
如果您只想为不同的类型运行一两行不同的代码,那么constexpr if可以让您不必使用enable_if就可以做到...
<cpp |keyword C++ ifstatement: begins theifstatement constexprifstatement: begins theconstexprifstatement (since C++17) constevalifstatement: begins theconstevalifstatement (since C++23) See also ifstatement:else constexprifstatement:constexpr(constexprifstatement) ...