devector

Header-only double ended vector implementation for efficient insertions/removals at both the start & end of it at the expense of an extra pointer.

Following C++ standard with slight modifications.

Currently C++11, C++14 coming next.

Now in Beta

Implementation details

devector keeps a dynamic array internally which it uses to store its objects. It differs from std::vector from the fact that begin() isn’t necessarily pointing to the start of the array, it’s instead up to the user to decide.

A simple visualisation:

image

In order to control where begin is placed, a third template parameter named OffsetBy is introduced which should have a method with the following signature:

size_t off_by(size_t free_blocks);

The one and only parameter is the count of free slots inside the array at any given moment the method is called.
It should return an integer which is going to be begin‘s offset from array_begin. You are free to make the method static, const, noexcept or whatever else you desire. The default implementation is this:

image

The offset is used upon reallocations, assignments of any sort, or shifting caused from operations such as insert, erase operator= etc…

A general rule of thumb is that whenever an operation has to move and/or copy things around, devector will automatically place them in the desired position according to the offset.

As a consequence of the above, if you make a custom OffsetBy class that always returns 0 as offset, the behavior should be exactly the same as std::vector.

If needed in the future offset_by_traits shall also be introduced.

Which methods differ from std::vector and how

This container implements the very same methods the standard does, following exception safety rules, iterator validity and even thread-safety wherever possible. The differences are in fact:

Any operation that causes shifting, like insert at any position besides begin & end, erase at any position besides begin & end, emplace at any position besides begin & end will now not only invalidate the iterators following pos(the position iterator each of these functions take as argument), but the whole [begin,end) set except for very specific situations which you shouldn’t rely upon.

New methods are introduced, here is a list:

  • resize_front()
  • resize_back()
  • push_front()
  • pop_front()
  • emplace_front()
  • get_offset_by()

each of which does exactly the same their x_back() pair does but for the front instead. resize() still exists and defaults to resize_back().

Every constructor or operation that previously had an optional allocator_type& alloc parameter now also has an optional offset_by_type& off_by type.

Collaborate

You are absolutely welcome to report bugs, contribute by solving issues, or even help build C++14, C++17, and C++20 versions.

About

Licenced under MIT Licence.

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