| | | 1 | | // Licensed to the .NET Foundation under one or more agreements. |
| | | 2 | | // The .NET Foundation licenses this file to you under the MIT license. |
| | | 3 | | |
| | | 4 | | using System.Diagnostics.CodeAnalysis; |
| | | 5 | | |
| | | 6 | | namespace System.Text.Json.Serialization |
| | | 7 | | { |
| | | 8 | | /// <summary> |
| | | 9 | | /// Customizes the System.Text.Json behavior of a union type. |
| | | 10 | | /// </summary> |
| | | 11 | | /// <remarks> |
| | | 12 | | /// <para> |
| | | 13 | | /// A type is recognized by System.Text.Json as a union when it carries |
| | | 14 | | /// <c>System.Runtime.CompilerServices.UnionAttribute</c> (the marker emitted by |
| | | 15 | | /// the C# compiler for union declarations). Applying |
| | | 16 | | /// <see cref="JsonUnionAttribute"/> on its own does not make a type a union — the |
| | | 17 | | /// attribute is silently ignored when no union marker is present, and the |
| | | 18 | | /// type is serialized as a regular object. |
| | | 19 | | /// </para> |
| | | 20 | | /// <para> |
| | | 21 | | /// On a recognized union, this attribute is purely a customization knob — currently |
| | | 22 | | /// it lets the user plug in a per-type <see cref="TypeClassifier"/>. Recognized unions |
| | | 23 | | /// without this attribute receive the default JSON-value-based classifier. |
| | | 24 | | /// </para> |
| | | 25 | | /// <para> |
| | | 26 | | /// Case types are discovered automatically from the union's public single-parameter |
| | | 27 | | /// constructors. For types where convention-based discovery does not work, use |
| | | 28 | | /// contract customization to populate <see cref="Metadata.JsonTypeInfo.UnionCases"/> |
| | | 29 | | /// and set the deconstructor/constructor delegates on |
| | | 30 | | /// <see cref="Metadata.JsonTypeInfo{T}"/>. |
| | | 31 | | /// </para> |
| | | 32 | | /// </remarks> |
| | | 33 | | [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct, AllowMultiple = false, Inherited = false)] |
| | | 34 | | public sealed class JsonUnionAttribute : JsonAttribute |
| | | 35 | | { |
| | | 36 | | /// <summary> |
| | | 37 | | /// Gets or sets the type of a <see cref="JsonTypeClassifierFactory"/> implementation |
| | | 38 | | /// used to classify JSON payloads during deserialization. |
| | | 39 | | /// </summary> |
| | | 40 | | /// <remarks> |
| | | 41 | | /// <para> |
| | | 42 | | /// When <see langword="null"/>, the built-in JSON value-shape classifier is used. |
| | | 43 | | /// It dispatches using the current JSON token kind rather than by inspecting object |
| | | 44 | | /// property names or other payload contents. |
| | | 45 | | /// </para> |
| | | 46 | | /// <para> |
| | | 47 | | /// The specified type must derive from <see cref="JsonTypeClassifierFactory"/> |
| | | 48 | | /// and have a public parameterless constructor. |
| | | 49 | | /// </para> |
| | | 50 | | /// <para> |
| | | 51 | | /// The classifier is not invoked for JSON <see cref="JsonTokenType.Null"/> |
| | | 52 | | /// payloads. The null token is dispatched directly to the union's constructor delegate, |
| | | 53 | | /// which yields the canonical null union when at least one case is nullable |
| | | 54 | | /// and otherwise throws a <see cref="JsonException"/>. See |
| | | 55 | | /// <see cref="JsonTypeClassifier"/> for details. |
| | | 56 | | /// </para> |
| | | 57 | | /// </remarks> |
| | | 58 | | [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)] |
| | 0 | 59 | | public Type? TypeClassifier { get; set; } |
| | | 60 | | } |
| | | 61 | | } |
| | | 62 | | |