Consider this:
#include <set>
template <typename T, T val>
class sample {
public:
// Return val for new elements.
T& at(unsigned i) {
auto o = _set.insert(val);
return *o.first;
}
private:
std::set<T> _set;
};
class s {
public:
constexpr s() = default;
};
int main() {
constexpr s val;
sample<s, val> o2;
return 0;
}
gcc -std=c++11 doesn't compile.
non-type.cc: In function ‘int main()’:
non-type.cc:24:18: error: ‘class s’ is not a valid type for a template non-type parameter
sample<s, val> o2;
As mentioned in the comment, I want new elements of 'set' are initialized to 'val'. As val is constant, it looks reasonable expectation!
Can someone please tell me how I can achieve it?
It looks like what you want to do is possible, but requires C++20.
From the docs
Until C++20 a "non-type parameter" needs to be one of
- std::nullptr_t (since C++11); - an integral type; - a pointer type (to object or to function); - a pointer to member type (to member object or to member function); - an enumeration type.
Having a non-type parameter of a custom type seems to not be available at the moment unless you have access to a compiler that already has that feature.
Collected from the Internet
Please contact [email protected] to delete if infringement.
Comments