Stack and Heap

Start with the idea

A stack frame commonly holds fixed-size local values or handles. Heap allocations support storage whose size or lifetime needs more flexibility and require an owner to release them. Box, Vec, and String are heap values with a small stack handle, which is exactly why moving one is cheap and cloning one is not.

A function call commonly creates a stack frame containing local values or handles whose sizes are known to the compiler. Heap allocation supports values whose storage needs to live independently of a particular stack frame or whose size is chosen at runtime. But ownership and physical location are separate questions. A Vec<T> value holds a pointer, length, and capacity as a small handle; its elements usually live in a heap allocation. Moving the Vec handle transfers ownership of that allocation without copying every element.

Cloning a Vec is different: it creates another allocation and copies or clones elements.