veque

The double-ended vector

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A very fast C++17 container combining the best features of std::vector and std::deque

"In Most Cases, Prefer Using deque (Controversial)"

-Herb Sutter, GotW #54

veque is an allocator-aware, efficient container with interface matching both std::vector and std::deque. Its data layout is very similar to std::vector, but with unused storage maintained both before and after the used storage.

Features

• Like std::vector, veque is an ordered container in cache-friendly, array-compatible contiguous memory. That makes the data compatible with C APIs, pointer iteration, gsl::span, and similar.
• Like std::deque, veque allows fast insertion/deletion from the front of the container
• Because veque can resize from both sides, insertions and erasures from arbitrary locations will be twice as fast on average, because there are two choices for what data to shift.

Usage

The complete API documentation may be viewed here.

The interface for veque maintains the entire interface for std::vector, allowing veque to be considered as a drop-in replacement. (See tradeoffs)

In addition, veque provides the following additional functions:

std::deque interface:

• push_front()
• emplace_front()
• pop_front()

End-specific resizing:

• resize_front()
• resize_back() (Same as resize(), to match std::vector and std::deque behavior)
• capacity_front()
• capacity_back() (Same as capacity(), to match std::vector and std::deque behavior)
• capacity_full()
• reserve(size_type, size_type)

Strong exception guarantee pop-and-return, courtesy C++17:

• pop_back_element()
• pop_front_element()

In the spirit of C++20, it is reasonable to ask for the size as a signed type:

• ssize()

Tradeoffs

Is veque better than std::vector in every conceivable way? No. But the tradeoffs are appealing.

• veque is a bit more eager to preallocate memory than a typical std::vector implementation, to anticipate resizing from either end. (New - configurable via traits class!)
• insert() and erase() function calls should be assumed to invalidate all iterators and references, since the resizing could happen from either direction. By comparison, the same std::vector and std::deque operations will sometimes only invalidate some of the iterators and references. (New - configurable via traits class!)
• veque<bool> is not specialized. Whether that makes it better or worse is up to you.

Why "veque"?

As a developer, I am not good at naming things.

double_ended_vector?

dextor?

To do:

• Perhaps C++14 support?