# replaceVertices(at:_:) Replaces the entire contents of a vertex buffer synchronously on the CPU. ``` final func replaceVertices(at index: Int, _ body: @_lifetime(0: copy 0) (inout MutableRawSpan) throws(E) -> R) throws(E) -> R where E : Error, R : ~Copyable ``` ## Parameters `index` The vertex buffer index to replace. `body` A closure that receives a mutable span over the buffer’s bytes and fully populates it. ## Discussion You pass a closure that receives a mutable span representing the contents of the vertex buffer. Upon entry the buffer’s contents are undefined; the closure is responsible for populating it with valid data. This span is valid only for the duration of the closure. > Throws: Any error thrown by `body`. --- 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)