Add ToString extensions

CHANGELOG.md

@@ -19,3 +19,5 @@
 - Add async versions of `Result<T>.Match` and `Result<T>.Switch`.
 
 - Rename `Result<T>.ToType` to `To` and allow attempting to convert to non-derived types.
+
+- Add ToString extensions supporting `IFormattable`.

src/Rascal.Tests/ResultExtensionsTests.cs

@@ -1,9 +1,28 @@
+using System.Globalization;
 using Rascal.Errors;
 
 namespace Rascal.Tests;
 
 public class ResultExtensionsTests
 {
+    [Fact]
+    public void ToString_UsesFormat_ForOk()
+    {
+        var result = Ok(15);
+        var str = result.ToString("b", CultureInfo.InvariantCulture);
+
+        str.ShouldBe("Ok { 1111 }");
+    }
+
+    [Fact]
+    public void ToString_ReturnsErrorMessage_ForErr()
+    {
+        var result = Err<int>("error");
+        var str = result.ToString("b", CultureInfo.InvariantCulture);
+
+        str.ShouldBe("Error { error }");
+    }
+
     [Fact]
     public void Unnest()
     {

src/Rascal/ResultExtensions.cs

@@ -7,6 +7,43 @@ namespace Rascal;
 /// </summary>
 public static class ResultExtensions
 {
+    /// <summary>
+    /// Returns a string representation of the result
+    /// using a specified format and <see cref="IFormatProvider"/> to format an ok value.
+    /// </summary>
+    /// <param name="result">The result to return a string representation of.</param>
+    /// <param name="format">The format to use.</param>
+    /// <param name="formatProvider">The provider to use to format the ok value.</param>
+    /// <typeparam name="T">The type of the ok value in the result.</typeparam>
+    public static string ToString<T>(this Result<T> result, string? format, IFormatProvider? formatProvider)
+        where T : IFormattable =>
+        result.Match(
+            x => $"Ok {{ {x.ToString(format, formatProvider)} }}",
+            e => $"Error {{ {e} }}"
+        );
+
+    /// <summary>
+    /// Returns a string representation of the result
+    /// using a specified format to format an ok value.
+    /// </summary>
+    /// <param name="result">The result to return a string representation of.</param>
+    /// <param name="format">The format to use.</param>
+    /// <typeparam name="T">The type of the ok value in the result.</typeparam>
+    public static string ToString<T>(this Result<T> result, string format)
+        where T : IFormattable =>
+        result.ToString(format, null);
+
+    /// <summary>
+    /// Returns a string representation of the result
+    /// using a specified <see cref="IFormatProvider"/> to format an ok value.
+    /// </summary>
+    /// <param name="result">The result to return a string representation of.</param>
+    /// <param name="formatProvider">The provider to use to format the ok value.</param>
+    /// <typeparam name="T">The type of the ok value in the result.</typeparam>
+    public static string ToString<T>(this Result<T> result, IFormatProvider formatProvider)
+        where T : IFormattable =>
+        result.ToString(null, formatProvider);
+
     /// <summary>
     /// Takes a result containing another result and un-nests the inner result.
     /// </summary>