listlike

Listlike is a term used in computer science and software development to describe objects whose behavior resembles that of a list. An object that is listlike typically supports operations such as iteration, accessing elements by position, and reporting its size. The concept is informal and depends on duck typing rather than a rigid inheritance. In practice, a listlike object can be treated as a sequence of elements for purposes such as looping over items or indexing into them, even if the object is not an actual language list.

In languages with explicit interfaces, a listlike object may implement a standard interface analogous to a list or sequence. For example, in Python, the collections.abc.Sequence interface defines the minimum protocol for listlike objects: __len__, __getitem__, and __iter__. Tuples, lists, strings, and many array-like collections are listlike because they support length, indexing, and iteration. Some objects are only partially listlike, offering indexing but not mutability or full iteration.

In practice, libraries and APIs often accept any listlike input to improve flexibility. They may convert the input to a concrete list internally or process it via iteration. Listlike is often discussed alongside terms such as array-like, sequence, or collection, each emphasizing different aspects of the data structure.

Alternative usage notes: in JavaScript, array-like objects have a numeric length property and indexed elements but may lack array methods, while truly array-like generically resembles a list in its access patterns.