MoveOnlyMoveOnly

MoveOnlyMoveOnly is a term used in programming to describe a type whose instances can be transferred between owners by move operations but cannot be copied. The primary goal is to enforce exclusive ownership of a resource, such as memory, a file handle, or a network connection, and to prevent unintended sharing that could lead to resource duplication or leaks.

Typical characteristics: non-copyable but moveable; implements a move constructor and move assignment operator, often deleting the copy constructor and copy assignment operator. A move-only type may provide operations to reset, release, or swap its resource. After a move, the source object is left in a valid but unspecified state; the resource is considered transferred to the destination.

Common design patterns: wrapper types that manage resources (RAII objects) use move semantics to transfer ownership. In C++, std::unique_ptr is the canonical example; in other languages, similar ideas exist under the concept of ownership and moves. The goal is to avoid expensive copies and to guarantee a single owner of the resource at any time.

Usage considerations: storage in containers is allowed for move-only types if the container supports moving; be mindful of interactions with APIs that require copyable arguments; ensure move semantics are exception-safe; provide a clear transfer mechanism and a safe default state for moved-from objects.

Impact and alternatives: Move-only types complement reference counting or shared ownership where copying is needed; but they can complicate APIs that expect copyable arguments; if sharing is required, consider smart pointers with shared ownership or pass-by-reference.

See also: Move semantics, Copy semantics, RAII, Smart pointer, Resource management.