subdataWithRange

SubdataWithRange is a data-handling operation used in several programming frameworks to obtain a new data object containing a contiguous subset of bytes from an existing data object. The range is defined by a starting index and a length or by a continuous index interval. The resulting object is typically separate from the source, enabling isolated processing of the selected bytes.

In Objective-C's Foundation framework,NSData provides the method -subdataWithRange:, which accepts an NSRange and returns a new NSData containing the bytes in that range. The original data is not modified. If the range exceeds the bounds of the receiver, an exception may be raised depending on the environment.

In Swift, the Data type offers subdata(in:) to produce a new Data instance from a specific range. The parameter can be expressed as a Range or ClosedRange over Data.Index, commonly written as 5..<15 for bytes 5 through 14. The result is a separate copy of the requested bytes; the original Data remains unchanged. Swift's copy-on-write storage can affect performance characteristics but does not change the observable behavior.

Use cases include parsing binary formats, extracting headers, or isolating a payload segment without duplicating the entire buffer. Bounds checking is important: invalid ranges can lead to runtime errors in Objective-C or crashes in Swift if using invalid indices, though Swift also provides bounds-checked initializers and methods.

See also: Data, NSData, NSRange, Range, ClosedRange, copy-on-write semantics.