# BNNSGraphContextSetDynamicShapes(_:_:_:_:) Specifies the dynamic shapes for a graph and, if possible, infers, the output shapes. ``` func BNNSGraphContextSetDynamicShapes(_ context: bnns_graph_context_t, _ function: UnsafePointer?, _ shapes_count: Int, _ shapes: UnsafeMutablePointer) -> Int32 ``` ## Parameters `context` The graph context. `function` The function. Specify as `nil` if the graph only contains one function. `shapes_count` The number of elements in the `shapes` array. `shapes` An array of input and output shapes in the same order as you pass to [`BNNSGraphContextExecute(_:_:_:_:_:_:)`](/documentation/Accelerate/BNNSGraphContextExecute(_:_:_:_:_:_:)). On input, this function reads input shapes with a nonzero rank, and uses the constant or default value from the source model for input shapes with a zero rank. The function generates an error for shapes with a nonzero value that doesn’t match the source model. On output, the function sets output shapes with a nonzero rank to the upper bounds of the expected output shape. If the function can’t deduce the output shape because it depends on the input data values, the value of `shapes[idx].size[d]` is zero. ## Return Value - `0` on success if all tensor shapes were exactly determined. That is, the workspace size is exact. ## Discussion - `1` on success if one or more tensor shapes are merely bounds, but no tensor is unbounded. That is, the workspace size is bounded. - `2` on success if one or more tensor shapes are unbounded and BNNS will allocate workspace memory during execution. - A negative value indicates an error. ## Discussion Don’t call this function while existing calls to [`BNNSGraphContextExecute(_:_:_:_:_:_:)`](/documentation/Accelerate/BNNSGraphContextExecute(_:_:_:_:_:_:)) are running. For example, the following code sets the dynamic shapes for an example graph context, specifies the output shape, and updates the context’s required workspace size. ```swift var inputShape: [UInt64] = [1024, 1, 1] let rank = inputShape.count var outputShape = [UInt64](repeating: 0, count: rank) let result = outputShape.withUnsafeMutableBufferPointer { output in inputShape.withUnsafeMutableBufferPointer { input in var shapes = [ bnns_graph_shape_t(rank: rank, shape: output.baseAddress!), bnns_graph_shape_t(rank:rank, shape: input.baseAddress!) ] return BNNSGraphContextSetDynamicShapes(context, nil, shapes.count, &shapes) } } // Prints "[1024, 1, 1]". print(outputShape) ``` On return, the output shape contains the correct size for the input shape, and a subsequent call to [`BNNSGraphContextGetWorkspaceSize(_:_:)`](/documentation/Accelerate/BNNSGraphContextGetWorkspaceSize(_:_:)) returns the correct workspace 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)