.. Sequences/Concepts//Bidirectional Sequence |20 Bidirectional Sequence ====================== Description ----------- A |Bidirectional Sequence| is a |Forward Sequence| whose iterators model |Bidirectional Iterator|. Refinement of ------------- |Forward Sequence| Expression requirements ----------------------- In addition to the requirements defined in |Forward Sequence|, for any |Bidirectional Sequence| ``s`` the following must be met: +---------------------------+-----------------------------------+---------------------------+ | Expression | Type | Complexity | +===========================+===================================+===========================+ | ``begin::type`` | |Bidirectional Iterator| | Amortized constant time | +---------------------------+-----------------------------------+---------------------------+ | ``end::type`` | |Bidirectional Iterator| | Amortized constant time | +---------------------------+-----------------------------------+---------------------------+ | ``back::type`` | Any type | Amortized constant time | +---------------------------+-----------------------------------+---------------------------+ Expression semantics -------------------- |Semantics disclaimer...| |Forward Sequence|. +---------------------------+-----------------------------------------------------------------------+ | Expression | Semantics | +===========================+=======================================================================+ | ``back::type`` | The last element in the sequence; see |back|. | +---------------------------+-----------------------------------------------------------------------+ Models ------ * |vector| * |range_c| See also -------- |Sequences|, |Forward Sequence|, |Random Access Sequence|, |Bidirectional Iterator|, |begin| / |end|, |back|