Merge pull request #567 from christophercalm/result-select-linq-query…

…-enable

added select overload with projection for result

CSharpFunctionalExtensions.Tests/ResultTests/Extensions/SelectTests.cs

@@ -0,0 +1,51 @@
+using FluentAssertions;
+using Xunit;
+
+namespace CSharpFunctionalExtensions.Tests.ResultTests.Extensions;
+public class SelectTests
+{
+    [Fact]
+    public void Select_returns_new_result()
+    {
+        Result<MyClass> result = new MyClass { Property = "Some value" };
+
+        Result<string> result2 = result.Select(x => x.Property);
+
+        result2.IsSuccess.Should().BeTrue();
+        result2.GetValueOrDefault().Should().Be("Some value");
+    }
+
+    [Fact]
+    public void Select_returns_no_value_if_no_value_passed_in()
+    {
+        Result<MyClass> result = Result.Failure<MyClass>("error message");
+
+        Result<MyClass> result2 = result.Select(x => x);
+
+        result2.IsSuccess.Should().BeFalse();
+        result2.GetValueOrDefault().Should().Be(default);
+    }
+
+    [Fact]
+    public void Result_Error_Select_from_class_to_struct_retains_Error()
+    {
+        Result.Failure<string>("error message").Select(_ => 42).IsSuccess.Should().BeFalse();
+        Result.Failure<string>("error message").Select(_ => 42).Error.Should().Be("error message");
+    }
+
+    [Fact]
+    public void Result_can_be_used_with_linq_query_syntax()
+    {
+        Result<string> name = "John";
+
+        Result<string> upper = from x in name select x.ToUpper();
+
+        upper.IsSuccess.Should().BeTrue();
+        upper.GetValueOrDefault().Should().Be("JOHN");
+    }
+
+    private class MyClass
+    {
+        public string Property { get; set; }
+    }
+}

CSharpFunctionalExtensions/Result/Methods/Extensions/Select.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace CSharpFunctionalExtensions
+{
+    public static partial class ResultExtensions
+    {
+        /// <summary>
+        ///     This method should be used in linq queries. We recommend using Map method.
+        /// </summary>
+        public static Result<K> Select<T, K>(in this Result<T> result, Func<T, K> selector)
+        {
+            return result.Map(selector);
+        }
+    }
+}