ArrayTuple: Initialization of larger structures

[xqms]

Started from mosra/magnum#505. Here's a reproducing example using just Corrade:

#include <Corrade/Containers/ArrayTuple.h>
#include <Corrade/Containers/ArrayView.h>
#include <Corrade/Utility/Debug.h>

using namespace Corrade;

int main(int argc, char** argv)
{
    Containers::ArrayView<std::pair<unsigned int, unsigned int>> arr;

    Containers::ArrayTuple tuple{
        {Containers::ValueInit, 4, arr}
    };

    for(std::size_t i = 0; i < arr.size(); ++i)
    {
        Utility::Debug{} << i;
        if(arr[i].second != 0)
            Utility::Debug{} << "Yes!";
    }

    return 0;
}

Valgrind gives warnings about uninitialized memory after half of the array. I believe the problem is this line:

corrade/src/Corrade/Containers/ArrayTuple.cpp

Lines 280 to 283 in 1114af5

	/* If the item has a default constructor, call it on each element */
	if(items[i]._constructor)
	for(std::size_t j = 0; j != items[i]._elementCount; ++j)
	items[i]._constructor(_data + offset + j*items[i]._elementAlignment);

where it should be items[i]._constructor(_data + offset + j*items[i]._elementSize); - at least that fixes the valgrind errors.

Probably a unit test with larger structures is required, that tests whether the memory has been correctly initialized.

[mosra]

Wow, that was a stupid mistake from me. Thanks for all the investigation and the PR 👍