# replaceTriangleIndices(_:) Fills the triangle index buffer using the given closure. ``` func replaceTriangleIndices(_ body: @_lifetime(0: copy 0) (inout MutableRawSpan) -> R) throws -> R where R : ~Copyable ``` ## Parameters `body` A closure that receives a mutable span over the buffer. ## Return Value The value returned by `body`. ## Discussion After the closure returns, the framework validates every vertex index against the vertex count. An out-of-range index causes a throw. > Throws: If any vertex index is outside `[0, vertexCount)`. --- 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)