flat_set constructor with ordered_unique_range

[dariomt@…]

I would expect that the constructors taking a ordered_unique_range_t would assert that the passed range indeed is sorted and unique according to the sorting criteria of the flat_set.

e.g. I'd expect the following code to assert, but instead it prints 0

#include <boost/container/flat_set.hpp>
#include <iostream>

using namespace std;
using namespace boost::container;

int main()
{
    auto l = {3, 2, 1};    
    flat_set<int> s (ordered_unique_range, l);
    cout << s.count(1) << endl;
}

I think the constructor should use std::is_sorted (or the Boost equivalent) to assert that the passed range indeed meets the specified ordered_unique_range.

std::is_sorted has complexity Linear in N, so with this change these constructors would keep their current complexity (which is also Linear in N) even when NDEBUG is not #defined.

[Ion Gaztañaga]

Thanks for the proposal. The check was easy to implement in constructors. In insert() it's really tricky as the input iterator's value_type needs to only be EmplaceConstructible and values are inserted quite differently, so insert() functions are left intact. Checks for constructors added in commit:

​https://github.com/boostorg/container/commit/fb1be6fa75c965c24a03a658c4990137e547d492