An alternative solution provided by the Standard Library is:
std::array<B, some_constant_value>
arr((std::copy(init.begin(),init.end(),(&arr)->begin()),arr));
Note that the argument of the constructor is enclosed by ((...))
, so that it
is correctly parsed as a comma-expression rather than as two arguments.
This solution relies upon the fact that B
is implicitly constructible from
A
. A short solution that will also work if the converting constructor is
made explicit is:
auto lamb =
[&init]() -> B { static size_t i = 0; return B(init[i++]); };
std::array<B, some_constant_value>
arr((std::generate((&arr)->begin(),(&arr)->end(),lamb),arr));
The following test program, built with GCC 4.7.2, clang 3.2 and Intel C++ 13.1.1,
(options -g -O0 -Wall -std=c++11
) illustrates both solutions:
#include <iostream>
#include <array>
#include <algorithm>
struct A
{
int _i = 42;
};
struct B
{
B(A x)
: _i(x._i){}
int _i;
};
struct C
{
explicit C(A x)
: _i(x._i){}
int _i;
};
using namespace std;
int main()
{
array<A, 10> init;
array<B, 10> arr((copy(init.begin(),init.end(),(&arr)->begin()),arr));
cout << "arr contains..." << endl;
for (size_t i = 0; i < arr.size(); ++i) {
cout << arr[i]._i << endl;
}
auto lamb =
[&init]() -> C { static size_t i = 0; return C(init[i++]); };
array<C, 10> brr((generate((&brr)->begin(),(&brr)->end(),lamb),brr));
cout << "brr contains..." << endl;
for (size_t i = 0; i < brr.size(); ++i) {
cout << brr[i]._i << endl;
}
return 0;
}