I need to be able to have any object that takes a single bool as a template parameter, and obtain the type of that object without the bool, so I can then create a similarly typed object but of a different bool.
This is what I came up with, but it does not compile. How can I achieve this aim please?
template<template<bool> typename ClassName, bool TheBool>
struct FT
{
using TYPE = ClassName;
};
template<bool X>
struct T {};
int main() {
T<true> t;
// Somehow get the type T (without the true) so I can then create a T<false> if I want...
using RawType = FT<decltype(t)>::TYPE;
RawType<false> f;
}
(I have searched beforehand but came up blanks, hence this question.)
CodePudding user response：
How about this:
#include <type_traits>
template<typename T, bool TheBool> struct FT;
template<template<bool> typename ClassName, bool origBool, bool TheBool>
struct FT< ClassName<origBool>, TheBool> {
typedef ClassName<TheBool> TYPE;
};
template<typename T, bool TheBool>
using FT_t=typename FT<T, TheBool>::TYPE;
template<bool X>
struct T {};
int main() {
T<true> t;
FT_t<decltype(t), false> f;
static_assert(std::is_same_v<decltype(f), T<false>>);
}
Perhaps some of your fruitless searches were due to imprecise terminology. "any object that takes a single bool as a template parameter" is not a meaningful C term. Objects don't have "template parameters". Templates have templates parameters. Furthermore, objects, types, and templates have specific meaninges. A template is not a type, a type is not a template. "a similarly typed object but of a different bool" also is not correct terminology, either.
CodePudding user response：
A little ugly, but this works:
template<bool NewBool, template<bool> typename ClassName, bool TheBool>
ClassName<NewBool> FT(const ClassName<TheBool>&);
template<bool X>
struct T {};
int main() {
T<true> t;
decltype(FT<false>(t)) f;
}