# OutputSpan `OutputSpan` is a reference to a contiguous region of memory that starts with some number of initialized `Element` instances followed by uninitialized memory. It provides operations to access the items it stores, as well as to add new elements and to remove existing ones. ``` @frozen struct OutputSpan where Element : ~Copyable ``` ## Topics ### Initializers [`init()`](/documentation/Swift/OutputSpan/init()) Create an OutputSpan with zero capacity. [`init(buffer: UnsafeMutableBufferPointer, initializedCount: Int)`](/documentation/Swift/OutputSpan/init(buffer:initializedCount:)-3tbg3) Unsafely create an OutputSpan over partly-initialized memory. [`init(buffer: borrowing Slice>, initializedCount: Int)`](/documentation/Swift/OutputSpan/init(buffer:initializedCount:)-vie3) Unsafely create an OutputSpan over partly-initialized memory. ### Instance Properties [`let capacity: Int`](/documentation/Swift/OutputSpan/capacity) The total number of elements that this output span can contain. [`var count: Int`](/documentation/Swift/OutputSpan/count) The number of initialized elements in this span. [`var freeCapacity: Int`](/documentation/Swift/OutputSpan/freeCapacity) The number of additional elements that can be added to this span. [`var indices: Range.Index>`](/documentation/Swift/OutputSpan/indices) The range of initialized indices for this `OutputSpan`. [`var isEmpty: Bool`](/documentation/Swift/OutputSpan/isEmpty) A Boolean value indicating whether the span is empty. [`var isFull: Bool`](/documentation/Swift/OutputSpan/isFull) A Boolean value indicating whether the span is full. [`var mutableSpan: MutableSpan`](/documentation/Swift/OutputSpan/mutableSpan) Exclusively borrow the underlying initialized memory for mutation. [`var span: Span`](/documentation/Swift/OutputSpan/span) Borrow the underlying initialized memory for read-only access. ### Instance Methods [`func append(consuming Element)`](/documentation/Swift/OutputSpan/append(_:)) Append a single element to this span. [`func append(repeating: Element, count: Int)`](/documentation/Swift/OutputSpan/append(repeating:count:)) Repeatedly append an element to this span. [`func finalize(for: Slice>) -> Int`](/documentation/Swift/OutputSpan/finalize(for:)-5utkq) Consume the output span and return the number of initialized elements. [`func finalize(for: UnsafeMutableBufferPointer) -> Int`](/documentation/Swift/OutputSpan/finalize(for:)-83pw0) Consume the output span and return the number of initialized elements. [`func removeAll()`](/documentation/Swift/OutputSpan/removeAll()) Remove all this span’s elements and return its memory to the uninitialized state. [`func removeLast() -> Element`](/documentation/Swift/OutputSpan/removeLast()) Remove the last initialized element from this span. [`func removeLast(Int)`](/documentation/Swift/OutputSpan/removeLast(_:)) Remove the last n elements of this span, returning the memory they occupy to the uninitialized state. [`func swapAt(OutputSpan.Index, OutputSpan.Index)`](/documentation/Swift/OutputSpan/swapAt(_:_:)) Exchange the elements at the two given indices. [`func swapAt(unchecked: OutputSpan.Index, unchecked: OutputSpan.Index)`](/documentation/Swift/OutputSpan/swapAt(unchecked:unchecked:)) Exchange the elements at the two given indices. [`func withUnsafeMutableBufferPointer((UnsafeMutableBufferPointer, inout Int) throws(E) -> R) throws(E) -> R`](/documentation/Swift/OutputSpan/withUnsafeMutableBufferPointer(_:)) Call the given closure with the unsafe buffer pointer addressed by this OutputSpan and a mutable reference to its count of initialized elements. ### Subscripts [`subscript(OutputSpan.Index) -> Element`](/documentation/Swift/OutputSpan/subscript(_:)) Accesses the element at the specified index. [`subscript(unchecked _: OutputSpan.Index) -> Element`](/documentation/Swift/OutputSpan/subscript(unchecked:)) Accesses the element at the specified index. ### Type Aliases [`typealias Index`](/documentation/Swift/OutputSpan/Index) The type that represents an initialized index in an `OutputSpan`. ### Default Implementations [Iterable Implementations](/documentation/Swift/OutputSpan/Iterable-Implementations) ## Relationships ### Conforms To [`Sendable`](/documentation/Swift/Sendable) [`ContiguousBytes`](/documentation/Foundation/ContiguousBytes) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`Iterable`](/documentation/Swift/Iterable) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)