As far as I can tell, the issue isn’t caused by map::emplace, but by pair‘s constructors: #include <map> struct A { A(int) {} A(A&&) = delete; A(A const&) = delete; }; int main() { std::pair<int, A> x(1, 4); // error } This code example doesn’t compile, neither with coliru’s g++4.8.1 nor with clang++3.5, which are … Read more
Tuples are available since .NET4.0 and support generics: Tuple<string, int> t = new Tuple<string, int>(“Hello”, 4); In previous versions you can use System.Collections.Generic.KeyValuePair<K, V> or a solution like the following: public class Pair<T, U> { public Pair() { } public Pair(T first, U second) { this.First = first; this.Second = second; } public T First … Read more
Actually, the code for pairs is exactly the same, since std::tuple has operator = with std::pair as an argument. num_letter = std::make_pair(10, ‘a’); std::tie(num, letter) = num_letter;
This is what priority_queue looks like: template< class T, class Container = std::vector<T>, class Compare = std::less<typename Container::value_type> > class priority_queue; In other words, CompareDist should be the third argument and the second argument should be the container (which has value_type), like the following: priority_queue<pair<int,int>,vector<pair<int,int>>,CompareDist> pq; Notice also, that priority_queue is what is called a … Read more
std::pair<int, int>::pair() constructor initializes the fields with default values (zero in case of int) and your struct Cell doesn’t (since you only have an auto-generated default constructor that does nothing). Initializing requires writing to each field which requires a whole lot of memory accesses that are relatively time consuming. With struct Cell nothing is done … Read more
With structured binding from C++17, you may directly do auto [lhsMinIt, lhsMaxIt] = std::minmax_element(lhs.begin(), lhs.end());
In terms of performance: it’s unlikely to change anything, you’re just sugar coating it. In terms of usability, I would rather use a custom struct, which can be declared this way (by the way): struct MyElement { int label; double value; }; I am a strong proponent of strong typing, and I much prefer a … Read more
Add another pair of braces. std::array<std::pair<int, int>, 2> ids = { { { 0, 1 }, { 1, 2 } } }; std::array<T, N> is an aggregate class containing a member of type T[N]. Usually, you can initialise that the same way you would a plain T[N] array, but when you’re dealing with a non-aggregate … 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
You are looking for std::nullopt instead of nullptr. std::vector<std::pair<int, std::optional<bool> > > vec1 = { {1, true}, {2,false}, {3,std::nullopt} };