Initialising std::pair, 3> >

Question

Can anyone advise on the correct syntax for the std::make_pair call in the std::vector::push_back call in the code below:

#include <array>
#include <vector>
#include <utility>

int main()
{
    typedef std::pair<double, double> PairType;
    std::vector<std::pair<double, std::array<PairType, 3> > > myVector;

    double Key = 0.0;
    PairType Pair1 = std::make_pair(1.0, 2.0);
    PairType Pair2 = std::make_pair(3.0, 4.0);
    PairType Pair3 = std::make_pair(5.0, 6.0);

    myVector.push_back(std::make_pair(Key, { Pair1, Pair2, Pair3 } )); // Syntax Error

    return 0;
}

The compiler (MS VS2015.2) cannot determine the type of the second argument in the std::make_pair call, which is understandable yet I don't know how to enlighten it.

Possible duplicate of [Why doesn't my template accept an initializer list](http://stackoverflow.com/questions/4757614/why-doesnt-my-template-accept-an-initializer-list) — LogicStuff, Oct 12 '16 at 09:42
Note that you don't need make_pair: `myVector.push_back({Key, { Pair1, Pair2, Pair3 } });` — Vaughn Cato, Oct 12 '16 at 14:12

score 3 · Accepted Answer · answered Oct 12 '16 at 09:42

3

It looks like the compiler cannot figure out that { Pair1, Pair2, Pair3 } is an std::array of three pairs. Specifying the type explicitly should work:

myVector.push_back(std::make_pair(Key, std::array<PairType,3>{ Pair1, Pair2, Pair3 } ));

Demo.

answered Oct 12 '16 at 09:42

Sergey Kalinichenko

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songyuanyao · Answer 2 · 2016-10-12T10:02:55.090

3

You could use std::experimental::make_array, if the compiler supports Library fundamentals v2:

using std::experimental::make_array;
myVector.push_back(std::make_pair(Key, make_array(Pair1, Pair2, Pair3) ));

LIVE from GCC

edited Oct 12 '16 at 10:02

answered Oct 12 '16 at 09:42

songyuanyao

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1

Or just write `make_array` as it is not that long. – Yakk - Adam Nevraumont Oct 12 '16 at 10:00
1

@Yakk With a `using std::experimental::make_array;`? Sure. – songyuanyao Oct 12 '16 at 10:03
no, write the implementation, if you do not have it. It is a short function. – Yakk - Adam Nevraumont Oct 12 '16 at 10:16

Initialising std::pair, 3> >

2 Answers2