Feature #2998
Updated by Junxiao Shi over 9 years ago
In `Block` abstraction, allow inserting an element at a specified position.
element_iterator
insert(element_const_iterator insert(element_iterator pos, const Block& element);
Change the parameter type and return type of `Block::erase` from `element_iterator` to `element_const_iterator`.
Parameter type is `element_const_iterator`, because both `find` and `elements_begin` return `element_const_iterator`, so that the caller is unable to obtain a `element_iterator`.
Using `element_const_iterator` is also consistent with C++11 APIs.
`std::vector<..>::insert` and `std::vector<..>::erase` installed with gcc46 on Ubuntu 12.04 does not take `const_iterator`.
This problem can be solved by internally converting from `elements_const_iterator` to `elements_iterator` [with `std::advance`](http://stackoverflow.com/a/3629059/3729203).
Compiler-feature detection should be performed to detect the necessity of this trick; this trick shall be wrapped in `#ifdef`.