Annex C (informative) Compatibility [diff]

[container.requirements]
Change: Complexity of size() member functions now constant.

Rationale: Lack of specification of complexity of size() resulted in divergent implementations with inconsistent performance characteristics.

Effect on original feature: Some container implementations that conform to C++ 2003 may not conform to the specified size() requirements in this International Standard.

Adjusting containers such as std​::​list to the stricter requirements may require incompatible changes.

[container.requirements]
Change: Requirements change: relaxation.

Rationale: Clarification.

Effect on original feature: Valid C++ 2003 code that attempts to meet the specified container requirements may now be over-specified.

Code that attempted to be portable across containers may need to be adjusted as follows:

• not all containers provide size(); use empty() instead of size() == 0;
• not all containers are empty after construction (array);
• not all containers have constant complexity for swap() (array).

[container.requirements]
Change: Requirements change: default constructible.

Rationale: Clarification of container requirements.

Effect on original feature: Valid C++ 2003 code that attempts to explicitly instantiate a container using a user-defined type with no default constructor may fail to compile.

[sequence.reqmts], [associative.reqmts]
Change: Signature changes: from void return types.

Rationale: Old signature threw away useful information that may be expensive to recalculate.

Effect on original feature: The following member functions have changed:

• erase(iter) for set, multiset, map, multimap
• erase(begin, end) for set, multiset, map, multimap
• insert(pos, num, val) for vector, deque, list, forward_­list
• insert(pos, beg, end) for vector, deque, list, forward_­list

Valid C++ 2003 code that relies on these functions returning void (e.g., code that creates a pointer to member function that points to one of these functions) will fail to compile with this International Standard.

[sequence.reqmts], [associative.reqmts]
Change: Signature changes: from iterator to const_­iterator parameters.

Rationale: Overspecification.

Effect on original feature: The signatures of the following member functions changed from taking an iterator to taking a const_­iterator:

• insert(iter, val) for vector, deque, list, set, multiset, map, multimap
• insert(pos, beg, end) for vector, deque, list, forward_­list
• erase(begin, end) for set, multiset, map, multimap
• all forms of list​::​splice
• all forms of list​::​merge

Valid C++ 2003 code that uses these functions may fail to compile with this International Standard.

[sequence.reqmts], [associative.reqmts]
Change: Signature changes: resize.

Rationale: Performance, compatibility with move semantics.

Effect on original feature: For vector, deque, and list the fill value passed to resize is now passed by reference instead of by value, and an additional overload of resize has been added.

Valid C++ 2003 code that uses this function may fail to compile with this International Standard.