#258 Adds new utility to provide substrings of a given string as Span<char> given a char delimeter. Language version updated to 7.2 due to need for ref Struct to utilize Span<T> as a field.

Author: Corey Floyd

src/JsonApiDotNetCore/Internal/SpanSplitter.cs

@@ -0,0 +1,64 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Linq;
+using JsonApiDotNetCore.Extensions;
+
+namespace JsonApiDotNetCore.Internal
+{
+    public readonly ref struct SpanSplitter
+    {
+        private readonly ReadOnlySpan<char> _span;
+        private readonly List<int> _delimeterIndexes;
+        private readonly List<Tuple<int, int>> _substringIndexes;
+
+        public int Count => _substringIndexes.Count();
+        public ReadOnlySpan<char> this[int index] => GetSpanForSubstring(index + 1);
+
+        public SpanSplitter(ref string str, char delimeter)
+        {
+            _span = str.AsSpan();
+            _delimeterIndexes = str.IndexesOf(delimeter).ToList();
+            _substringIndexes = new List<Tuple<int, int>>();
+            BuildSubstringIndexes();
+        }
+
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override bool Equals(object obj) => throw new NotSupportedException();
+
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override int GetHashCode() => throw new NotSupportedException();
+
+        [EditorBrowsable(EditorBrowsableState.Never)]
+        public override string ToString() => throw new NotSupportedException();
+
+        private ReadOnlySpan<char> GetSpanForSubstring(int substringNumber)
+        {
+            if (substringNumber > Count)
+            {
+                throw new ArgumentOutOfRangeException($"There are only {Count} substrings given the delimeter and base string provided");
+            }
+
+            var indexes = _substringIndexes[substringNumber - 1];
+            return _span.Slice(indexes.Item1, indexes.Item2);
+        }
+        
+        private void BuildSubstringIndexes()
+        {
+            var start = 0;
+            var end = 0;
+            foreach (var index in _delimeterIndexes)
+            {
+                end = index;
+                if (start > end) break;
+                _substringIndexes.Add(new Tuple<int, int>(start, end - start));
+                start = ++end;
+            }
+
+            if (end <= _span.Length)
+            {
+                _substringIndexes.Add(new Tuple<int, int>(start, _span.Length - start));
+            }
+        }
+    }
+}

src/JsonApiDotNetCore/JsonApiDotNetCore.csproj

@@ -21,6 +21,7 @@
     <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="$(AspNetCoreVersion)" />
     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="$(EFCoreVersion)" />
     <PackageReference Include="Microsoft.Extensions.Logging" Version="$(MicrosoftLoggingVersion)" />
+    <PackageReference Include="System.Memory" Version="4.5.0-preview2-26406-04" />
     <PackageReference Include="System.ValueTuple" Version="$(TuplesVersion)" />
   </ItemGroup>
 
@@ -31,6 +32,12 @@
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
     <DocumentationFile>bin\Release\netstandard2.0\JsonApiDotNetCore.xml</DocumentationFile>
   </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Release|netstandard2.0|AnyCPU'">
+    <LangVersion>7.2</LangVersion>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(TargetFramework)|$(Platform)'=='Debug|netstandard2.0|AnyCPU'">
+    <LangVersion>7.2</LangVersion>
+  </PropertyGroup>
   <ItemGroup Condition="$(IsWindows)=='true'">
     <PackageReference Include="docfx.console" Version="2.33.0" />
   </ItemGroup>

test/UnitTests/Internal/SpanSplitterTests.cs

@@ -0,0 +1,107 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using JsonApiDotNetCore.Internal;
+using Xunit;
+
+namespace UnitTests.Internal
+{
+    public class SpanSplitterTests : SpanSplitterTestsBase
+    {
+        [Fact]
+        public void StringWithDelimeterSplitsIntoCorrectNumberSubstrings()
+        {
+            GivenMultipleCommaDelimetedString();
+            WhenSplittingIntoSubstrings();
+            AssertCorrectSubstringsReturned();
+        }
+
+        [Fact]
+        public void StringWithSingleDelimeterSplitsIntoCorrectNumberSubstrings()
+        {
+            GivenSingleCommaDelimetedString();
+            WhenSplittingIntoSubstrings();
+            AssertCorrectSubstringsReturned();
+        }
+
+        [Fact]
+        public void StringWithNoDelimeterSplitsIntoSingleSubstring()
+        {
+            GivenNonCommaDelimetedString();
+            WhenSplittingIntoSubstrings();
+            AssertCorrectSubstringsReturned();
+        }
+
+        [Fact]
+        public void StringWithDelimeterAtEndSplitsIntoCorrectSubstring()
+        {
+            GivenStringWithCommaDelimeterAtEnd();
+            WhenSplittingIntoSubstrings();
+            AssertCorrectSubstringsReturned();
+        }
+
+        [Fact]
+        public void StringWithDelimeterAtBeginningSplitsIntoCorrectSubstring()
+        {
+            GivenStringWithCommaDelimeterAtBeginning();
+            WhenSplittingIntoSubstrings();
+            AssertCorrectSubstringsReturned();
+        }
+    }
+
+    public abstract class SpanSplitterTestsBase
+    {
+        private string _baseString;
+        private char _delimeter;
+        private readonly List<string> _substrings = new List<string>();
+
+        protected void GivenMultipleCommaDelimetedString()
+        {
+            _baseString = "This,Is,A,TestString";
+            _delimeter = ',';
+        }
+
+        protected void GivenSingleCommaDelimetedString()
+        {
+            _baseString = "This,IsATestString";
+            _delimeter = ',';
+        }
+
+        protected void GivenNonCommaDelimetedString()
+        {
+            _baseString = "ThisIsATestString";
+        }
+
+        protected void GivenStringWithCommaDelimeterAtEnd()
+        {
+            _baseString = "This,IsATestString,";
+            _delimeter = ',';
+        }
+
+        protected void GivenStringWithCommaDelimeterAtBeginning()
+        {
+            _baseString = "/api/v1/articles";
+            _delimeter = '/';
+        }
+
+        protected void WhenSplittingIntoSubstrings()
+        {
+            SpanSplitter spanSplitter;
+            spanSplitter = new SpanSplitter(ref _baseString, _delimeter);
+            for (var i = 0; i < spanSplitter.Count; i++)
+            {
+                var span = spanSplitter[i];
+                _substrings.Add(span.ToString());
+            }
+        }
+
+        protected void AssertCorrectSubstringsReturned()
+        {
+            Assert.NotEmpty(_substrings);
+            var stringSplitArray = _baseString.Split(_delimeter);
+            Assert.Equal(stringSplitArray.Length, _substrings.Count);
+            Assert.True(stringSplitArray.SequenceEqual(_substrings));
+        }
+    }
+}