MLXArray (Data, Dtype) constructor , DType size. (#158)

* Array init, Dtype codable and tests

Signed-off-by: Valentin Roussellet <[email protected]>

Source/MLX/DType.swift

@@ -24,7 +24,7 @@ import Numerics
 /// - ``MLXArray/asType(_:stream:)-6d44y``
 /// - ``MLXArray/asType(_:stream:)-4eqoc``
 /// - ``MLXArray/init(_:dtype:)``
-public enum DType: Hashable, Sendable {
+public enum DType: Hashable, Sendable, CaseIterable {
     case bool
     case uint8
     case uint16
@@ -105,6 +105,23 @@ public enum DType: Hashable, Sendable {
         default: false
         }
     }
+
+    public var size: Int {
+        mlx_dtype_size(cmlxDtype)
+    }
+}
+
+extension DType: Encodable {
+    public func encode(to encoder: any Encoder) throws {
+        try self.cmlxDtype.rawValue.encode(to: encoder)
+    }
+}
+
+extension DType: Decodable {
+    public init(from decoder: any Decoder) throws {
+        let rawValue = try UInt32(from: decoder)
+        self.init(mlx_dtype(rawValue: rawValue))
+    }
 }
 
 /// Protocol for types that can provide a ``DType``

Source/MLX/MLXArray+Init.swift

@@ -11,6 +11,13 @@ private func shapePrecondition(shape: [Int]?, count: Int) {
     }
 }
 
+private func shapePrecondition(shape: [Int]?, byteCount: Int, type: DType) {
+    if let shape {
+        let total = shape.reduce(1, *) * type.size
+        precondition(total == byteCount, "shape \(shape) total \(total)B != \(byteCount)B (actual)")
+    }
+}
+
 extension MLXArray {
 
     /// Initalizer allowing creation of scalar (0-dimension) `MLXArray` from an `Int32`.
@@ -436,6 +443,25 @@ extension MLXArray {
             })
     }
 
+    /// Initalizer allowing creation of `MLXArray` from a `Data`  buffer values with
+    /// an optional shape and an explicit DType.
+    /// ### See Also
+    /// - <doc:initialization>
+    public convenience init(_ data: Data, _ shape: [Int]? = nil, dtype: DType) {
+        self.init(
+            data.withUnsafeBytes { ptr in
+                shapePrecondition(shape: shape, byteCount: data.count, type: dtype)
+                precondition(data.count % dtype.size == 0)
+                let shape = shape ?? [data.count / dtype.size]
+                return mlx_array_new_data(
+                    ptr.baseAddress!, shape.asInt32, shape.count.int32, dtype.cmlxDtype)
+            })
+    }
+
+    public convenience init(data: MLXArrayData) {
+        self.init(data.data, data.shape, dtype: data.dType)
+    }
+
     /// Create a ``DType/complex64`` scalar.
     /// - Parameters:
     ///   - real: real part
@@ -448,6 +474,7 @@ extension MLXArray {
     public convenience init(_ value: Complex<Float>) {
         self.init(real: value.real, imaginary: value.imaginary)
     }
+
 }
 
 // MARK: - Expressible by literals

Tests/MLXTests/MLXArray+InitTests.swift

@@ -12,8 +12,30 @@ class MLXArrayInitTests: XCTestCase {
         setDefaultDevice()
     }
 
-    // MARK: - Creation
+    // MARK: - Dtype
+    func testDtypeSize() {
+        // Checking that the size of the dtype matches the array's itemsize
+        for dtype in DType.allCases {
+            XCTAssertEqual(MLXArray(Data(), dtype: dtype).itemSize, dtype.size)
+        }
+    }
 
+    func testDtypeCodable() {
+        let encoder = JSONEncoder()
+        let decoder = JSONDecoder()
+        // Test encoding / decoding round trip
+        for dtype in DType.allCases {
+            do {
+                let json: Data = try encoder.encode(dtype)
+                let decoded = try decoder.decode(DType.self, from: json)
+                XCTAssertEqual(decoded, dtype)
+            } catch {
+                XCTFail("Encoding / decoding failed")
+            }
+        }
+    }
+
+    // MARK: - Creation
     func testInt() {
         // array creation with Int -- we want it to produce .int32
         let a1 = MLXArray(500)
@@ -87,8 +109,10 @@ class MLXArrayInitTests: XCTestCase {
     func testData() {
         let data = Data([1, 2, 3, 4])
         let a = MLXArray(data, [2, 2], type: UInt8.self)
+        let b = MLXArray(data, [2, 2], dtype: DType.uint8)
         let expected = MLXArray(UInt8(1) ... 4, [2, 2])
         assertEqual(a, expected)
+        assertEqual(b, expected)
     }
 
     func testUnsafeRawPointer() {

Tests/MLXTests/MLXArrayTests.swift

@@ -129,6 +129,13 @@ class MLXArrayTests: XCTestCase {
         }
     }
 
+    func testAsDataRoundTrip() {
+        let a = MLXArray(0 ..< 16, [4, 4])
+        let arrayData = a.asData(access: .copy)
+        let result = MLXArray(arrayData.data, arrayData.shape, dtype: arrayData.dType)
+        assertEqual(a, result)
+    }
+
     func testAsDataNonContiguous() {
         // buffer with holes (last dimension has stride of 2 and
         // thus larger storage than it physically needs)