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Fix class invariant comment. In this implementation default constructed deque make no allocation so in that case start and finish are singular iterators.

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Ion Gaztañaga
2025-07-30 23:57:26 +02:00
parent ba82a1da7d
commit e680bd79a2
2 changed files with 3 additions and 7 deletions
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4
doc/container.qbk
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@@ -481,7 +481,7 @@ inserted predominantly on one extreme (e.g. pushed at one extreme and popped fro
To avoid unbounded memory waste, Boost.Container's `devector` uses a different strategy:
* If elements are inserted near a extreme and there is free space on that extreme, the insertion is performed
without any additional data movement (only the elements between the insertion point and the extreme are moved.
without any additional data movement (only the elements between the insertion point and the extreme are moved).
* If elements are inserted near one extreme and the free space on that extreme is exhausted, all existing elements
are relocated (moved) to the center of the internal memory buffer. This makes room in the exhausted extreme
@@ -492,7 +492,7 @@ To avoid unbounded memory waste, Boost.Container's `devector` uses a different s
relocations must be limited ('relocation limit') and a reallocation (allocation of a new memory buffer) will be
performed if the load-factor of the container defined as (size()/length_of_buffer) surpasses the relocation limit (see
Lars Greger Nordland Hagen's [@http://larshagencpp.github.io/blog/2016/05/22/devector "Double-ended vector - is it useful?"]
article for more details.
article for more details).
* This approach offers a reasonable balance between a reasonable memory overhead and performance.

6
include/boost/container/deque.hpp
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@@ -91,9 +91,6 @@ namespace dtl {
// i.cur is a pointer in the range [i.first, i.last). NOTE:
// the implication of this is that i.cur is always a dereferenceable
// pointer, even if i is a past-the-end iterator.
// Start and Finish are always nonsingular iterators. NOTE: this means
// that an empty deque must have one node, and that a deque
// with N elements, where N is the buffer size, must have two nodes.
// For every node other than start.node and finish.node, every element
// in the node is an initialized object. If start.node == finish.node,
// then [start.cur, finish.cur) are initialized objects, and
@@ -255,8 +252,7 @@ class deque_iterator
offset > 0 ? (offset / block_size)
: (-difference_type((-offset - 1) / block_size) - 1);
this->priv_set_node(this->m_node + node_offset, size_type(block_size));
this->m_cur = this->m_first +
(offset - node_offset * block_size);
this->m_cur = this->m_first + (offset - node_offset * block_size);
}
return *this;
}