On Saturday 01 December 2001 10:41 am, you wrote:
I want to make this explanation short so I will skip details. In a nutshell, during destruction or resize, a destructor is explicitly called from a loop for each element which has been constructed. Obviously this is desireable much of the time, but it is true even if the element type has an *empty* destructor. This can take a lot of unecessary time, like 10's or even a few 100 milliseconds, which can make a big difference in, say, inspection software used in an industrial production line.
This isn't really a problem with the specification of std::vector, but is a quality-of-implementation issue. If one knows that the destructor is trivial, one can compile a version of the destruction/resize code that does not contain a destruction loop.
I wrote a replacement vector class which uses delete[] internally but otherwise acts like std::vector just to get around this problem. There are some drawbacks and limitations during resizing, but there are times when this behavior is essential.
Does it meet the criteria for std::vector with respect to reserve(n)? It
seems that would present a problem...
In any case, I believe the solution is this:
template<bool> truth_type {};
template<typename InputIterator>
inline void destruct_elements_in_range(
InputIterator first,
InputIterator last,
truth_type<true>)
{
// The elements in the range have trivial destructors, so do nothing
}
template<typename InputIterator>
inline void destruct_elements_in_range(
InputIterator first,
InputIterator last,
truth_type<false>)
{
typedef typename std::iterator_traits<InputIterator>::value_type T;
for(; first != last; ++first) {
T* victim = &(*first);
victim->~T();
}
}
template<typename T>
class vector {
private:
void destruct_elements() {
destruct_elements_in_range(begin(), end(),
truth_type
Unfortunately, containers like the graph boost library use std::vector as containers and that is hardcoded. So the destructor for a graph might take 100 or 200 ms, when it should take almost nothing because there is nothing dangerous which really needs to be cleaned up.
Most Boost libraries that use containers allow you to supply your own container. Doug