Relaxing the Requirements for the Constant Time Versions of erase_begin and erase_end

[ldeng-ustc]

Currently, the constant time versions of erase_begin and erase_end are only applied when value_type is a scalar type. However, this requirement is overly restrictive.

For example, in the case of std::pair<int, int>, the current circular_buffer requires O(n) time to perform erase_end, which is actually unnecessary.

The O(n) version of erase seems to simply destruct elements. Therefore, would it be possible to relax the condition for the fast erase versions from is_scalar<value_type> to is_trivially_destructible, allowing types like std::pair<int, int> or other user-defined simple types to benefit from the faster erase_begin and erase_end?