# constantData(at:) Returns a pointer to an inline, constant-data argument within the argument buffer. ``` func constantData(at index: Int) -> UnsafeMutableRawPointer ``` ## Parameters `index` The index of an inline, constant-data argument within the argument buffer. The value corresponds to either the index ID of a declaration in Metal Shading Language (MSL) or the [`index`](/documentation/Metal/MTLArgumentDescriptor/index) property of an [`MTLArgumentDescriptor`](/documentation/Metal/MTLArgumentDescriptor) instance. ## Return Value A pointer to the location in the buffer to which you should write the constant data. ## Discussion Constants declared contiguously in the Metal shading language (in an array or structure) are contiguous in memory. You can encode contiguous ranges of inlined constant data through a pointer to the first constant. To encode inlined constant data into the argument buffer, perform a memory copy operation from your data’s source pointer to the returned destination pointer. ```swift let sourceConstants: [SourceConstants] = [ // Inlined constant data. /* ... */ ] let destinationPointer = abEncoder.constantData(: 0) destinationPointer.copyBytes(from: sourceConstants, count: MemoryLayout.size) ``` --- 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)