ubiq_trick.cpp

#include <type_traits>

template<int> struct int_constant {}; 
template<char> struct char_constant {}; 

inline constexpr struct ubiq
{
  template<class T>
  constexpr operator T() const noexcept
  { return T{}; }
} ubiq_;

template<auto X, template<auto> class T>
auto match(T<X>) -> decltype(X);

template<template<auto> class Trait>
using nttp_t = decltype(match(Trait<ubiq_>{}));

static_assert(std::is_same_v<decltype(match(int_constant<42>{})), int>);
static_assert(std::is_same_v<nttp_t<int_constant>, int>);
static_assert(std::is_same_v<nttp_t<char_constant>, char>);

int main(){}