As stated in P0174: The is_literal type trait offers negligible value to generic code, as what is really needed is the ability to know that a specific construction would produce constant initialization. The core term of a literal type having at least one constexpr constructor is too weak to be used meaningfully. Basically, what it’s … Read more
The reason this fails is because when you specify foo<Movable>, the function you’re binding to is: void foo(Movable&&) // *must* be an rvalue { } However, the value passed by std::bind will not be an rvalue, but an lvalue (stored as a member somewhere in the resulting bind functor). That, is the generated functor is … Read more
No, it doesn’t. The capacity of a vector never decreases. That isn’t mandated by the standard but it’s so both in standard library implementations of VC++ and g++. In order to set the capacity just enough to fit the size, use the famous swap trick vector<T>().swap(foo); In C++11 standard, you can do it more explicitly: … Read more
If you only need to ask “Is this variant of type X ?” for a single type X, then I recommend that you prefer std::holds_alternative over std::variant::index because the line of code is easier to read and will not have to be updated if the index of the type in the variant changes in the … Read more
Let’s go over the conditions as they appear: If const T isn’t const (const doesn’t really apply to function types since functions aren’t objects), and T isn’t a reference (const doesn’t apply to references either for the same reason), it’s a function type. int (or any other non-function-non-reference type) wouldn’t fit in because is_const<const int>::value … Read more
If the invocable is a pointer to a member function, then you need to do one of these: (arg1->*f)(arg2,…); (arg1.*f)(arg2,…); Depending on what arg1 is. INVOKE (and its official library counterpart std::invoke) was pretty much designed to simplify such messes. You’d use std::invoke to support the caller of your code passing any callable, and not … Read more
std::mem_fun is deprecated. std::mem_fn can do everything it does, and it does it more conveniently. The relation between the two is the same as the relation between std::bind1st/std::bind2nd and the C++11 std::bind. Both std::mem_fn and std::bind were developed and mastered after std::bind1st and std::mem_fun were made into the C++98 Standard. So that means we had … Read more
std::pair provides pre-written constructors and comparison operators. This also allows them to be stored in containers like std::map without you needing to write, for example, the copy constructor or strict weak ordering via operator < (such as required by std::map). If you don’t write them you can’t make a mistake (remember how strict weak ordering … Read more
#include <map> Problem solved.
I came here seeking for this answer but i found this distance function takes 2 iterators and returns an index cout << distance(mymap.begin(),mymap.find(“198765432”)); hope this helps 😀