(No version information available, might only be in Git)
A Deque (pronounced “deck”) is a sequence of values in a contiguous buffer that grows and shrinks automatically. The name is a common abbreviation of “double-ended queue” and is used internally by Ds\Queue.
Two pointers are used to keep track of a head and a tail. The pointers can “wrap around” the end of the buffer, which avoids the need to move other values around to make room. This makes shift and unshift very fast — something a Ds\Vector can’t compete with.
Accessing a value by index requires a translation between the index and its
corresponding position in the buffer:
((head + position) % capacity).
$capacity) : void
$glue] ) : string
$rotations) : void
$length] ) : Ds\Deque