foreach

Foreach is a control flow construct used in many programming languages to iterate over the elements of a collection, such as arrays, lists, or maps. The loop applies a block of code to each element in the sequence, typically abstracting away manual index handling and boundary checks.

Syntax and language variations are common. In Java and C#, for example, a common form is for (Type item : collection) { ... } or foreach (Type item in collection) { ... }. PHP uses foreach ($array as $value) { ... } and can also expose keys. JavaScript offers a for...of form (for (const item of array) { ... }) and, alternatively, Array.prototype.forEach. Python uses for item in collection: { ... }. While the exact syntax differs, the underlying idea is consistent: obtain each element in turn and execute the loop body.

Semantics can differ regarding modification. In many languages, the loop variable yields a value that does not automatically modify the original collection, and updating elements may require special syntax or additional indexing. Some languages allow iterating by reference or provide means to modify the underlying collection during iteration, while others prohibit structural changes to the collection while iterating.

Advantages of foreach include improved readability, reduced risk of off-by-one errors, and a concise pattern for applying an operation to every element. Limitations include limited access to element indices (unless the language provides a way to obtain them) and potential difficulties when the collection should be modified structurally during iteration.

Common uses are applying transformations or actions to each element, iterating over maps or key-value pairs, and performing operations without explicit index management. Foreach is widely supported, with language-specific variations and terminology such as for-each or foreach.