SetLength

SetLength is a term used in several programming languages to describe an operation that adjusts the declared length of a dynamic array or a string. The routine typically allocates or releases memory to match the new length and may initialize newly created elements to default values. Negative lengths are usually invalid and may raise an error.

In Pascal and its descendants such as Delphi and Free Pascal, SetLength is a standard procedure. It is used as SetLength(A, N) where A is a dynamic array (or string) and N is the desired length. If N is greater than the current length, the array is extended and new elements receive default initialization. If N is smaller, elements beyond N are discarded, and existing elements up to N are preserved.

Other languages provide similar functionality under different names or mechanisms. For example, some environments offer a separate resize function or require creating a new array and copying elements. In languages with immutable string types, resizing a string may involve creating a new string rather than mutating the original one. Length is often exposed as a property or determined by a separate operation rather than a built-in mutator.

Semantics and considerations vary by language design. Resizing may move the underlying memory and invalidate references to elements, and the operation might perform element-wise copying. Many implementations guarantee that existing elements up to the new length are preserved, while the handling of newly created elements depends on the type system and initialization rules.