shrinkto

Shrinkto is a programming concept used to reduce the allocated memory capacity of a dynamic container to match its current size. The term is most often encountered in the form shrink_to_fit in language standard libraries, though the exact name and behavior vary by language.

In C++, containers like std::vector and std::basic_string expose shrink_to_fit as a non-binding request to reduce capacity to fit size. The standard notes that the request may have no effect; an implementation may decide to skip reallocation. When it does take effect, it typically reallocates memory and moves the existing elements to a new buffer, potentially freeing unused capacity.

In Rust, Vec<T> provides shrink_to_fit to reduce capacity to match length, which may trigger a reallocation. Other languages have similar mechanisms under different names, such as shrink or shrinkToFit.

Practical guidance: shrinkto can help reduce memory usage after the container has grown and then shed many elements, but it can be expensive due to allocations and element movement. Because the operation is not guaranteed to free memory immediately, it should be used when memory pressure exists or a predictable footprint is required.

Limitations and alternatives: Not all containers support shrink_to_fit, and behavior is implementation-dependent. A common alternative to guarantee a smaller capacity is to copy the elements into a freshly constructed container and swap it with the old one.

Related concepts include capacity, size, and general memory management, as well as language-specific implementations such as shrink_to_fit in C++ and Vec::shrink_to_fit in Rust.