Merge pull request #169 from aka-nse/feature/as-readonly-span

[Proposal] Adds TextSpan.AsReadOnlySpan()

Author: nblumhardt

src/Superpower/Model/TextSpan.cs

@@ -233,6 +233,16 @@ public string ToStringValue()
             return Source!.Substring(Position.Absolute, Length);
         }
 
+        /// <summary>
+        /// Compute the string value of this span and return the view of source directly.
+        /// </summary>
+        /// <returns>A view of string with the value of this span.</returns>
+        public ReadOnlySpan<char> AsReadOnlySpan()
+        {
+            EnsureHasValue();
+            return Source!.AsSpan(Position.Absolute, Length);
+        }
+
         /// <summary>
         /// Compare the contents of this span with <paramref name="otherValue"/>.
         /// </summary>

src/Superpower/Superpower.csproj

@@ -25,4 +25,7 @@
   <ItemGroup>
     <None Include="..\..\asset\Superpower-White-400px.png" Pack="true" Visible="false" PackagePath="" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
+    <PackageReference Include="System.Memory" Version="4.6.3" />
+  </ItemGroup>
 </Project>

test/Superpower.Tests/Model/TextSpanTest.cs

@@ -0,0 +1,27 @@
+using System;
+using Superpower.Model;
+using Xunit;
+
+namespace Superpower.Tests.Model
+{
+    public class TextSpanTest
+    {
+        [Theory]
+        [InlineData("hello", 0, 5, "hello")]
+        [InlineData("hello", 1, 3, "ell")]
+        [InlineData("hello", 2, 0, "")]
+        [InlineData("The quick brown fox jumps over the lazy dog", 9, 7, " brown ")]
+        public void AsReadOnlySpanWorks(string input, int start, int length, string expected)
+        {
+            var span = new TextSpan(input).Skip(start).First(length);
+            var readOnlySpan = span.AsReadOnlySpan();
+            Assert.Equal(expected, readOnlySpan.ToString());
+        }
+
+        [Fact]
+        public void AsReadOnlySpanEnsureHasValue()
+        {
+            Assert.Throws<InvalidOperationException>(() => TextSpan.None.AsReadOnlySpan());
+        }
+    }
+}