propagateoncontainermoveassignment
Propagate on container move assignment, often referred to by the trait propagate_on_container_move_assignment, is a component of the C++ standard library allocator framework. It indicates whether an allocator should be propagated from a source container to a destination container during move assignment.
- The trait is part of the allocator_traits infrastructure. It is represented as a nested type that
- Its value determines whether the allocator of the source container is moved to the destination container
- During move assignment of standard library containers (such as vector, deque, list, map, etc.), the library
- If the trait value is true, the destination adopts the source’s allocator (the allocator from the
Default behavior and customization
- For the default std::allocator, the trait typically resolves to false, meaning no propagation occurs unless a
- Custom allocators can provide or specialize propagate_on_container_move_assignment to indicate desired behavior, enabling allocator propagation in move
- The propagate_on_container_move_assignment trait is used in concert with other allocator_traits such as propagate_on_container_copy_assignment and propagate_on_container_swap, which
- Together, these traits define allocator-aware behavior for containers, ensuring that operations on containers interact predictably with
- Developers can query allocator_traits<Alloc>::propagate_on_container_move_assignment::value at compile time to write generic container code that respects allocator propagation
- Correct implementation of the trait helps maintain consistency with the standard library’s allocator-aware container semantics.