added TryRecover extensions

README.md

@@ -69,9 +69,9 @@ Result<T> Bar()
 ```csharp
 Result<int> result = GetResult();
 
-var value = result
+string value = result
-    .Append("new")
+    .Append("new") // -> Result<(int, string)>
-    .Map((i, s) => $"{s} result {i}")
+    .Map((i, s) => $"{s} result {i}") // -> Result<string>
     .Match(
         onSuccess: x => x,
         onFailure: err => err.ToString()
@@ -81,6 +81,17 @@ var value = result
 Result<int> GetResult() => Result.Success(1);
 ```
 
+#### Recover from failure
+
+```csharp
+Result<string> failed = new NotImplementedException();
+
+Result<string> result = failed.TryRecover(err => err.Type == "System.NotImplementedException"
+    ? "recovered"
+    : err);
+// result with value: "recovered"
+```
+
 ### Try
 
 ```csharp
@@ -99,9 +110,9 @@ int SomeFunction() => 1;
 ### Ensure
 
 ```csharp
-var value = GetValue();
+int? value = GetValue();
-Result<int> result = Ensure.That(value)
+Result<int> result = Ensure.That(value) // -> Ensure<int?>
-    .NotNull()
+    .NotNull() // -> Ensure<int>
     .Satisfies(i => i < 100)
     .Result();
 

Railway.SourceGenerator/EnsureExtensionsExecutor.cs

@@ -41,22 +41,46 @@ public sealed class EnsureExtensionsExecutor : IGeneratorExecutor
 
         var sb = new StringBuilder();
 
-        sb.AppendLine($"#region Satisfies");
+        sb.AppendLine("#region Satisfies");
         errorGenerationDefinitions.ForEach(def => GenerateSatisfiesExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
         sb.AppendLine("#endregion");
 
-        sb.AppendLine($"#region NotNull");
+        sb.AppendLine("#region NotNull");
         errorGenerationDefinitions.ForEach(def => GenerateNotNullExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
         sb.AppendLine("#endregion");
 
-        sb.AppendLine($"#region NotEmpty");
+        sb.AppendLine("#region NotEmpty");
         errorGenerationDefinitions.ForEach(def => GenerateNotEmptyExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
         sb.AppendLine("#endregion");
 
+        sb.AppendLine("#region NotWhitespace");
+        errorGenerationDefinitions.ForEach(def => GenerateNotWhitespaceExtensions(sb, def.ErrorParameterDecl, def.ErrorValueExpr));
+        sb.AppendLine("#endregion");
 
         return sb.ToString();
     }
 
+    private void GenerateNotWhitespaceExtensions(StringBuilder sb, string errorParameterDecl, string errorValueExpr)
+    {
+        string defaultErrorExpr = "?? Error.New(DefaultErrorType, $\"Value {{{ensure.ValueExpression}}} is empty or consists exclusively of white-space characters.\")";
+
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(EnsureExtensionsExecutor)}}", "1.0.0.0")]
+        public static Ensure<string> NotWhitespace(this in Ensure<string> ensure, {{errorParameterDecl}})
+        {
+            return ensure.State switch
+            {
+                ResultState.Success => string.IsNullOrWhiteSpace(ensure.Value)
+                    ? new({{errorValueExpr}} {{defaultErrorExpr}}, ensure.ValueExpression)
+                    : new(ensure.Value!, ensure.ValueExpression),
+                ResultState.Error => new(ensure.Error!, ensure.ValueExpression),
+                _ => throw new EnsureNotInitializedException(nameof(ensure))
+            };
+        }
+        """);
+    }
+
     private void GenerateNotEmptyExtensions(StringBuilder sb, string errorParameterDecl, string errorValueExpr)
     {
         string defaultErrorExpr = "?? Error.New(DefaultErrorType, $\"Value {{{ensure.ValueExpression}}} is empty.\")";

Railway.SourceGenerator/ExtensionsMethodGenerator.cs

@@ -17,6 +17,7 @@ public class ExtensionsMethodGenerator : IIncrementalGenerator
         new ResultMapExecutor(),
         new ResultBindExecutor(),
         new ResultTapExecutor(),
+        new ResultTryRecoverExecutor(),
         new ResultAppendExecutor(),
         new TryExtensionsExecutor(),
         new EnsureExtensionsExecutor(),

Railway.SourceGenerator/ResultTryRecoverExecutor.cs

@@ -0,0 +1,86 @@
+using System.Collections.Immutable;
+using System.Linq;
+using System.Text;
+using Microsoft.CodeAnalysis;
+
+namespace Just.Railway.SourceGen;
+
+internal sealed class ResultTryRecoverExecutor : ResultExtensionsExecutor
+{
+    protected override string ExtensionType => "TryRecover";
+    protected override void GenerateMethodsForArgCount(StringBuilder sb, int argCount)
+    {
+        if (argCount > 1) return;
+        
+        var templateArgNames = Enumerable.Repeat("T", argCount)
+            .ToImmutableArray();
+
+        string methodTemplateDecl = GenerateTemplateDecl(templateArgNames);
+        string resultTypeDef = GenerateResultTypeDef(templateArgNames);
+
+        sb.AppendLine($"#region {resultTypeDef}");
+
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static {{resultTypeDef}} TryRecover{{methodTemplateDecl}}(this in {{resultTypeDef}} result, Func<Error, {{resultTypeDef}}> recover)
+        {
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => recover(result.Error!),
+                _ => throw new ResultNotInitializedException(nameof(result))
+            };
+        }
+        """);
+
+        GenerateAsyncMethods("Task", sb, templateArgNames, resultTypeDef, methodTemplateDecl);
+        GenerateAsyncMethods("ValueTask", sb, templateArgNames, resultTypeDef, methodTemplateDecl);
+
+        sb.AppendLine("#endregion");
+    }
+    private static void GenerateAsyncMethods(string taskType, StringBuilder sb, ImmutableArray<string> templateArgNames, string resultTypeDef, string methodTemplateDecl)
+    {
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static async {{taskType}}<{{resultTypeDef}}> TryRecover{{methodTemplateDecl}}(this {{taskType}}<{{resultTypeDef}}> resultTask, Func<Error, {{resultTypeDef}}> recover)
+        {
+            var result = await resultTask.ConfigureAwait(false);
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => recover(result.Error!),
+                _ => throw new ResultNotInitializedException(nameof(resultTask))
+            };
+        }
+        """);
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static async {{taskType}}<{{resultTypeDef}}> TryRecover{{methodTemplateDecl}}(this {{resultTypeDef}} result, Func<Error, {{taskType}}<{{resultTypeDef}}>> recover)
+        {
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => await recover(result.Error!).ConfigureAwait(false),
+                _ => throw new ResultNotInitializedException(nameof(result))
+            };
+        }
+        """);
+        sb.AppendLine($$"""
+        [PureAttribute]
+        [GeneratedCodeAttribute("{{nameof(ResultTryRecoverExecutor)}}", "1.0.0.0")]
+        public static async {{taskType}}<{{resultTypeDef}}> TryRecover{{methodTemplateDecl}}(this {{taskType}}<{{resultTypeDef}}> resultTask, Func<Error, {{taskType}}<{{resultTypeDef}}>> recover)
+        {
+            var result = await resultTask.ConfigureAwait(false);
+            return result.State switch
+            {
+                ResultState.Success => ({{resultTypeDef}})result.Value,
+                ResultState.Error => await recover(result.Error!).ConfigureAwait(false),
+                _ => throw new ResultNotInitializedException(nameof(resultTask))
+            };
+        }
+        """);
+    }
+}

Railway/Ensure.cs

@@ -34,18 +34,6 @@ public static partial class Ensure
             _ => throw new EnsureNotInitializedException(nameof(ensureTask))
         };
     }
-
-    [Pure] public static Ensure<string> NotWhitespace(this in Ensure<string> ensure, Error error = default!)
-    {
-        return ensure.State switch
-        {
-            ResultState.Success => string.IsNullOrWhiteSpace(ensure.Value)
-                ? new(error ?? Error.New(DefaultErrorType, $"Value {{{ensure.ValueExpression}}} is empty or consists exclusively of white-space characters."), ensure.ValueExpression)
-                : new(ensure.Value, ensure.ValueExpression),
-            ResultState.Error => new(ensure.Error!, ensure.ValueExpression),
-            _ => throw new EnsureNotInitializedException(nameof(ensure))
-        };
-    }
 }
 
 public readonly struct Ensure<T>

Railway/Result.cs

@@ -8,6 +8,7 @@ internal enum ResultState : byte
 
 public readonly partial struct Result : IEquatable<Result>
 {
+    internal SuccessUnit Value => new();
     internal readonly Error? Error;
     internal readonly ResultState State;
 
@@ -51,12 +52,17 @@ public readonly partial struct Result : IEquatable<Result>
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static implicit operator Result(Error error) => new(error ?? throw new ArgumentNullException(nameof(error)));
     [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result(Exception exception) => new(
+        new ExceptionalError(exception ?? throw new ArgumentNullException(nameof(exception))));
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static implicit operator Result<SuccessUnit>(Result result) => result.State switch
     {
         ResultState.Success => new(new SuccessUnit()),
         ResultState.Error => new(result.Error!),
         _ => throw new ResultNotInitializedException(nameof(result))
     };
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static explicit operator Result(SuccessUnit _) => new(null);
 
     [Pure] public bool IsSuccess => Error is null;
     [Pure] public bool IsFailure => Error is not null;
@@ -139,14 +145,20 @@ public readonly struct Result<T> : IEquatable<Result<T>>
         Error = default;
     }
 
-    [Pure] public static explicit operator Result(Result<T> result) => result.State switch
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static explicit operator Result(Result<T> result) => result.State switch
     {
         ResultState.Success => new(null),
         ResultState.Error => new(result.Error!),
         _ => throw new ResultNotInitializedException(nameof(result))
     };
-    [Pure] public static implicit operator Result<T>(Error error) => new(error);
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
-    [Pure] public static implicit operator Result<T>(T value) => new(value);
+    public static implicit operator Result<T>(Error error) => new(error);
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result<T>(Exception exception) => new(
+        new ExceptionalError(exception ?? throw new ArgumentNullException(nameof(exception))));
+    [Pure, MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static implicit operator Result<T>(T value) => new(value);
     [Pure] public bool IsSuccess => State == ResultState.Success;
     [Pure] public bool IsFailure => State == ResultState.Error;
 

Raliway.Tests/Results/GeneralUsage.cs

@@ -128,4 +128,33 @@ public class GeneralUsage
         // Then
         Assert.Equal("satisfied", result);
     }
+
+    [Fact]
+    public void RecoverResultFromFailureState()
+    {
+        // Given
+        Result<string> failed = new NotImplementedException();
+        // When
+        var result = failed.TryRecover(err => 
+        {
+            Assert.IsType<NotImplementedException>(err.ToException());
+            return "recovered";
+        });
+        // Then
+        Assert.True(result.IsSuccess);
+        Assert.Equal("recovered", result.Value);
+    }
+
+    [Fact]
+    public void WhenCanNotRecoverResultFromFailureState()
+    {
+        // Given
+        var error = Error.New("test");
+        Result<string> failed = new NotImplementedException();
+        // When
+        var result = failed.TryRecover(err => error);
+        // Then
+        Assert.True(result.IsFailure);
+        Assert.Equal(error, result.Error);
+    }
 }