Merge pull request #3 from wintoncode/result-types

Add result type.

Author: Choc13

.gitignore

@@ -3,5 +3,6 @@
 bin/
 obj/
 .vs/
+.vscode/
 *.suo
 *.user

Winton.DomainModelling.Abstractions.sln.DotSettings

@@ -34,9 +34,12 @@
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 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/OLD_ENGINE/@EntryValue">True</s:Boolean>
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+	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_FIELD_ATTRIBUTE_ON_SAME_LINE_EX/@EntryValue">NEVER</s:String>
 	<s:Boolean x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_ACCESSOR_ATTRIBUTE_ON_SAME_LINE/@EntryValue">False</s:Boolean>
+	<s:String x:Key="/Default/CodeStyle/CodeFormatting/CSharpFormat/PLACE_SIMPLE_EMBEDDED_STATEMENT_ON_SAME_LINE/@EntryValue">NEVER</s:String>
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@@ -456,6 +459,11 @@
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+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpKeepExistingMigration/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ECSharpPlaceEmbeddedOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EAlwaysTreatStructAsNotReorderableMigration/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002ECSharpPlaceAttributeOnSameLineMigration/@EntryIndexedValue">True</s:Boolean>
+	<s:Boolean x:Key="/Default/Environment/SettingsMigration/IsMigratorApplied/=JetBrains_002EReSharper_002EPsi_002ECSharp_002ECodeStyle_002ESettingsUpgrade_002EMigrateBlankLinesAroundFieldToBlankLinesAroundProperty/@EntryIndexedValue">True</s:Boolean>
 
 
 

src/Winton.DomainModelling.Abstractions/AsyncResultExtensions.cs

@@ -0,0 +1,79 @@
+// Copyright (c) Winton. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+
+namespace Winton.DomainModelling
+{
+    /// <summary>
+    ///     Extension methods for asynchronous results which make it possible to chain async results together
+    ///     using a fluent API in the same way as synchronous results.
+    /// </summary>
+    public static class AsyncResultExtensions
+    {
+        /// <summary>
+        ///     Invokes another result generating function which takes as input the data of this result
+        ///     if it is successful after it has been awaited.
+        /// </summary>
+        /// <remarks>
+        ///     If this result is a failure then this is a no-op and the original failure is retained.
+        ///     This is useful for chaining serial operations together that return results.
+        /// </remarks>
+        /// <typeparam name="TData">
+        ///     The type of data encapsulated by the result.
+        /// </typeparam>
+        /// <typeparam name="TNewData">
+        ///     The type of data in the new result.
+        /// </typeparam>
+        /// <param name="resultTask">
+        ///     The async result that this extension method is invoked on.
+        /// </param>
+        /// <param name="onSuccess">
+        ///     The function that is invoked if this result represents a success.
+        /// </param>
+        /// <returns>
+        ///     If this result is a success, then the result of <paramref>onSuccess</paramref> function;
+        ///     otherwise the original error.
+        /// </returns>
+        public static async Task<Result<TNewData>> Then<TData, TNewData>(
+            this Task<Result<TData>> resultTask,
+            Func<TData, Result<TNewData>> onSuccess)
+        {
+            Result<TData> result = await resultTask;
+            return result.Then(onSuccess);
+        }
+
+        /// <summary>
+        ///     Invokes another result generating function which takes as input the data of this result
+        ///     if it is successful after it has been awaited.
+        /// </summary>
+        /// <remarks>
+        ///     If this result is a failure then this is a no-op and the original failure is retained.
+        ///     This is useful for chaining serial operations together that return results.
+        /// </remarks>
+        /// <typeparam name="TData">
+        ///     The type of data encapsulated by the result.
+        /// </typeparam>
+        /// <typeparam name="TNewData">
+        ///     The type of data in the new result.
+        /// </typeparam>
+        /// <param name="resultTask">
+        ///     The async result that this extension method is invoked on.
+        /// </param>
+        /// <param name="onSuccess">
+        ///     The asynchronous function that is invoked if this result represents a success.
+        /// </param>
+        /// <returns>
+        ///     If this result is a success, then the result of <paramref>onSuccess</paramref> function;
+        ///     otherwise the original error.
+        /// </returns>
+        public static async Task<Result<TNewData>> Then<TData, TNewData>(
+            this Task<Result<TData>> resultTask,
+            Func<TData, Task<Result<TNewData>>> onSuccess)
+        {
+            Result<TData> result = await resultTask;
+            return await result.Then(onSuccess);
+        }
+    }
+}

src/Winton.DomainModelling.Abstractions/DomainException.cs

@@ -9,6 +9,7 @@ namespace Winton.DomainModelling
     /// <summary>
     ///     Represents domain errors.
     /// </summary>
+    [Obsolete("Prefer to return results with an Error instead.", false)]
     public class DomainException : Exception
     {
         /// <summary>

src/Winton.DomainModelling.Abstractions/EntityNotFoundException.cs

@@ -9,6 +9,7 @@ namespace Winton.DomainModelling
     /// <summary>
     ///     An error indicating that an entity could not be found.
     /// </summary>
+    [Obsolete("Prefer to return results with a NotFoundError instead.", false)]
     public class EntityNotFoundException : DomainException
     {
         private EntityNotFoundException(string message)

src/Winton.DomainModelling.Abstractions/Error.cs

@@ -0,0 +1,36 @@
+// Copyright (c) Winton. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
+
+namespace Winton.DomainModelling
+{
+    /// <summary>
+    ///     The base class of all errors in the domain model.
+    /// </summary>
+    /// <remarks>
+    ///     In a domain model it is better to explicitly model errors rather than throw exceptions.
+    ///     Errors are legitimate outcomes of operations in a domain model where an operation is
+    ///     not guaranteed to succeed. Errors can occur for several reasons, such as not being able
+    ///     to find a requested entity or because the inputs received were invalid.
+    ///     On the other hand, exceptions should be used in exceptional circumstances that have
+    ///     occurred due to factors outside of the domain model's control, e.g. network failures.
+    ///     In general, problems in the domain model should be modelled as errors and exceptions should
+    ///     be reserved for cases where the user cannot be given information on how to correct the problem.
+    /// </remarks>
+    public class Error
+    {
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="Error" /> class.
+        /// </summary>
+        /// <param name="detail">The detail that describes the error.</param>
+        /// <returns>A new instance of <see cref="Error" />.</returns>
+        public Error(string detail)
+        {
+            Detail = detail;
+        }
+
+        /// <summary>
+        ///     Gets the detail that describes the error.
+        /// </summary>
+        public string Detail { get; }
+    }
+}

src/Winton.DomainModelling.Abstractions/Failure.cs

@@ -0,0 +1,71 @@
+// Copyright (c) Winton. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
+
+using System;
+using System.Threading.Tasks;
+
+namespace Winton.DomainModelling
+{
+    /// <inheritdoc />
+    /// <summary>
+    ///     A result indicating a failure.
+    /// </summary>
+    public sealed class Failure<TData> : Result<TData>
+    {
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="Failure{TData}" /> class.
+        /// </summary>
+        /// <param name="error">The error that caused the result to be a failure.</param>
+        /// <returns>A new instance of <see cref="Failure{TData}" />.</returns>
+        public Failure(Error error)
+        {
+            Error = error;
+        }
+
+        /// <summary>
+        ///     Gets the error that caused the failure.
+        /// </summary>
+        public Error Error { get; }
+
+        /// <inheritdoc />
+        public override Result<TNewData> Combine<TOtherData, TNewData>(
+            Result<TOtherData> other,
+            Func<TData, TOtherData, TNewData> combineData,
+            Func<Error, Error, Error> combineErrors)
+        {
+            return other.Match<Result<TNewData>>(
+                otherData => new Failure<TNewData>(Error),
+                otherError => new Failure<TNewData>(combineErrors(Error, otherError)));
+        }
+
+        /// <inheritdoc />
+        public override T Match<T>(Func<TData, T> onSuccess, Func<Error, T> onFailure)
+        {
+            return onFailure(Error);
+        }
+
+        /// <inheritdoc />
+        public override Result<TNewData> Select<TNewData>(Func<TData, TNewData> selectData)
+        {
+            return new Failure<TNewData>(Error);
+        }
+
+        /// <inheritdoc />
+        public override Task<Result<TNewData>> Select<TNewData>(Func<TData, Task<TNewData>> selectData)
+        {
+            return Task.FromResult<Result<TNewData>>(new Failure<TNewData>(Error));
+        }
+
+        /// <inheritdoc />
+        public override Result<TNextData> Then<TNextData>(Func<TData, Result<TNextData>> onSuccess)
+        {
+            return new Failure<TNextData>(Error);
+        }
+
+        /// <inheritdoc />
+        public override Task<Result<TNextData>> Then<TNextData>(Func<TData, Task<Result<TNextData>>> onSuccess)
+        {
+            return Task.FromResult<Result<TNextData>>(new Failure<TNextData>(Error));
+        }
+    }
+}

src/Winton.DomainModelling.Abstractions/NotFoundError.cs

@@ -0,0 +1,22 @@
+// Copyright (c) Winton. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See LICENSE in the project root for license information.
+
+namespace Winton.DomainModelling
+{
+    /// <inheritdoc />
+    /// <summary>
+    ///     An error indicating that an entity could not be found.
+    /// </summary>
+    public class NotFoundError : Error
+    {
+        /// <summary>
+        ///     Initializes a new instance of the <see cref="NotFoundError" /> class.
+        /// </summary>
+        /// <param name="detail">The detail that describes the error.</param>
+        /// <returns>A new instance of <see cref="NotFoundError" />.</returns>
+        public NotFoundError(string detail)
+            : base(detail)
+        {
+        }
+    }
+}