Merge pull request #19 from rameel/memory-marshal-extensions

Add TryGetStringView and TryGetArrayView extensions to MemoryMarshal

Author: rameel

Ramstack.Structures.Tests/InteropServices/MemoryMarshalTests.cs

@@ -44,4 +44,99 @@ public void CreateArrayView()
             MemoryMarshal.CreateArrayView(array, 0, 5).Length,
             Is.EqualTo(5));
     }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetStringView()
+    {
+        const string Input = "0123456789";
+
+        var memory = Input.AsMemory();
+        Assert.That(memory.IsEmpty, Is.False);
+
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out var view), Is.True);
+        Assert.That(view, Is.EqualTo(Input));
+
+        memory = memory[1..];
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out view), Is.True);
+        Assert.That(view, Is.EqualTo(Input[1..]));
+        Assert.That(view.Length, Is.EqualTo(Input.Length - 1));
+
+        memory = memory[1..];
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out view), Is.True);
+        Assert.That(view, Is.EqualTo(Input[2..]));
+        Assert.That(view.Length, Is.EqualTo(Input.Length - 2));
+
+        memory = memory.Slice(3, 2);
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out view), Is.True);
+        Assert.That(view, Is.EqualTo(Input[5..7]));
+        Assert.That(view.Length, Is.EqualTo(2));
+
+        memory = memory[memory.Length..];
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out view), Is.True);
+        Assert.That(view.Length, Is.Zero);
+
+        memory = memory[..];
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out view), Is.True);
+        Assert.That(view.Length, Is.Zero);
+
+        memory = memory[..0];
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out view), Is.True);
+        Assert.That(view.Length, Is.Zero);
+
+        Assert.That(memory.IsEmpty, Is.True);
+    }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetStringView_Array_ReturnsFalse()
+    {
+        var memory = new char[10].AsMemory();
+        Assert.That(MemoryMarshal.TryGetStringView(memory, out var view), Is.False);
+        Assert.That(view.IsDefault, Is.True);
+    }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetArrayView()
+    {
+        var buffer = Enumerable.Range(0, 10).ToArray();
+        var memory = buffer.AsMemory();
+
+        Assert.That(MemoryMarshal.TryGetArrayView<int>(memory, out var view), Is.True);
+        Assert.That(view, Is.EquivalentTo(buffer));
+    }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetArrayView_EmptyArray()
+    {
+        var buffer = Array.Empty<int>();
+        var memory = buffer.AsMemory();
+
+        Assert.That(MemoryMarshal.TryGetArrayView<int>(memory, out var view), Is.True);
+        Assert.That(view, Is.EquivalentTo(buffer));
+    }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetArrayView_Default()
+    {
+        var memory = default(ReadOnlyMemory<int>);
+
+        Assert.That(MemoryMarshal.TryGetArrayView(memory, out var view), Is.True);
+        Assert.That(view, Is.EquivalentTo(Array.Empty<int>()));
+    }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetArrayView_Empty()
+    {
+        var memory = ReadOnlyMemory<int>.Empty;
+
+        Assert.That(MemoryMarshal.TryGetArrayView(memory, out var view), Is.True);
+        Assert.That(view, Is.EquivalentTo(Array.Empty<int>()));
+    }
+
+    [Test]
+    public static void ReadOnlyMemory_TryGetArrayView_String_ReturnsFalse()
+    {
+        var memory = "0123456789".AsMemory();
+        Assert.That(MemoryMarshal.TryGetArrayView(memory, out var view), Is.False);
+        Assert.That(view.IsDefault, Is.True);
+    }
 }

Ramstack.Structures/InteropServices/MemoryMarshalExtensions.cs

@@ -119,5 +119,50 @@ public static ArrayView<T> CreateArrayView<T>(T[] array, int index, int length)
 
             return new ArrayView<T>(array, index, length, unused: 0);
         }
+
+        /// <summary>
+        /// Attempts to get a <see cref="StringView"/> from the underlying memory buffer.
+        /// </summary>
+        /// <param name="memory">Read-only memory containing a block of characters.</param>
+        /// <param name="view">When this method returns, contains the <see cref="StringView"/>
+        /// retrieved from the underlying read-only memory buffer.</param>
+        /// <returns>
+        /// <see langword="true"/> if the method successfully retrieves the underlying string;
+        /// otherwise, <see langword="false"/>.
+        /// </returns>
+        public static bool TryGetStringView(ReadOnlyMemory<char> memory, out StringView view)
+        {
+            if (MemoryMarshal.TryGetString(memory, out var value, out var start, out var length))
+            {
+                view = new StringView(value, start, length, unused: 0);
+                return true;
+            }
+
+            view = default;
+            return false;
+        }
+
+        /// <summary>
+        /// Attempts to get a <see cref="StringView"/> from the underlying memory buffer.
+        /// </summary>
+        /// <typeparam name="T">The type of elements in the read-only memory buffer.</typeparam>
+        /// <param name="memory">Read-only memory buffer.</param>
+        /// <param name="view">When this method returns, contains the <see cref="ArrayView{T}"/>
+        /// retrieved from the underlying read-only memory buffer.</param>
+        /// <returns>
+        /// <see langword="true"/> if the underlying memory buffer represents an array segment;
+        /// otherwise, <see langword="false"/>.
+        /// </returns>
+        public static bool TryGetArrayView<T>(ReadOnlyMemory<T> memory, out ArrayView<T> view)
+        {
+            if (MemoryMarshal.TryGetArray(memory, out var segment))
+            {
+                view = segment;
+                return true;
+            }
+
+            view = default;
+            return false;
+        }
     }
 }