feat!: Use same type for flag metadata and event metadata

The spec describes two types(flag metadata, and event metadata) that are functionally the same. This PR
makes a breaking change to bring both of the types to use a generic ImmutableMetadata type.

- Rename BaseMetadata to Immutable, make sealed class and implement a empty constructor

Fixes: #234

Signed-off-by: Benjamin Evenson <2031163+benjiro@users.noreply.github.com>

src/OpenFeature/Model/FlagEvaluationDetails.cs

@@ -2,74 +2,74 @@
 
 namespace OpenFeature.Model
 {
-    /// <summary>
-    /// The contract returned to the caller that describes the result of the flag evaluation process.
-    /// </summary>
-    /// <typeparam name="T">Flag value type</typeparam>
-    /// <seealso href="https://github.com/open-feature/spec/blob/v0.7.0/specification/types.md#evaluation-details"/>
-    public sealed class FlagEvaluationDetails<T>
-    {
         /// <summary>
-        /// Feature flag evaluated value
+        /// The contract returned to the caller that describes the result of the flag evaluation process.
         /// </summary>
-        public T Value { get; }
+        /// <typeparam name="T">Flag value type</typeparam>
+        /// <seealso href="https://github.com/open-feature/spec/blob/v0.7.0/specification/types.md#evaluation-details"/>
+        public sealed class FlagEvaluationDetails<T>
+        {
+                /// <summary>
+                /// Feature flag evaluated value
+                /// </summary>
+                public T Value { get; }
 
-        /// <summary>
-        /// Feature flag key
-        /// </summary>
-        public string FlagKey { get; }
+                /// <summary>
+                /// Feature flag key
+                /// </summary>
+                public string FlagKey { get; }
 
-        /// <summary>
-        /// Error that occurred during evaluation
-        /// </summary>
-        public ErrorType ErrorType { get; }
+                /// <summary>
+                /// Error that occurred during evaluation
+                /// </summary>
+                public ErrorType ErrorType { get; }
 
-        /// <summary>
-        /// Message containing additional details about an error.
-        /// <para>
-        /// Will be <see langword="null" /> if there is no error or if the provider didn't provide any additional error
-        /// details.
-        /// </para>
-        /// </summary>
-        public string? ErrorMessage { get; }
+                /// <summary>
+                /// Message containing additional details about an error.
+                /// <para>
+                /// Will be <see langword="null" /> if there is no error or if the provider didn't provide any additional error
+                /// details.
+                /// </para>
+                /// </summary>
+                public string? ErrorMessage { get; }
 
-        /// <summary>
-        /// Describes the reason for the outcome of the evaluation process
-        /// </summary>
-        public string? Reason { get; }
+                /// <summary>
+                /// Describes the reason for the outcome of the evaluation process
+                /// </summary>
+                public string? Reason { get; }
 
-        /// <summary>
-        /// A variant is a semantic identifier for a value. This allows for referral to particular values without
-        /// necessarily including the value itself, which may be quite prohibitively large or otherwise unsuitable
-        /// in some cases.
-        /// </summary>
-        public string? Variant { get; }
+                /// <summary>
+                /// A variant is a semantic identifier for a value. This allows for referral to particular values without
+                /// necessarily including the value itself, which may be quite prohibitively large or otherwise unsuitable
+                /// in some cases.
+                /// </summary>
+                public string? Variant { get; }
 
-        /// <summary>
-        /// A structure which supports definition of arbitrary properties, with keys of type string, and values of type boolean, string, or number.
-        /// </summary>
-        public FlagMetadata? FlagMetadata { get; }
+                /// <summary>
+                /// A structure which supports definition of arbitrary properties, with keys of type string, and values of type boolean, string, or number.
+                /// </summary>
+                public ImmutableMetadata? FlagMetadata { get; }
 
-        /// <summary>
-        /// Initializes a new instance of the <see cref="FlagEvaluationDetails{T}"/> class.
-        /// </summary>
-        /// <param name="flagKey">Feature flag key</param>
-        /// <param name="value">Evaluated value</param>
-        /// <param name="errorType">Error</param>
-        /// <param name="reason">Reason</param>
-        /// <param name="variant">Variant</param>
-        /// <param name="errorMessage">Error message</param>
-        /// <param name="flagMetadata">Flag metadata</param>
-        public FlagEvaluationDetails(string flagKey, T value, ErrorType errorType, string? reason, string? variant,
-            string? errorMessage = null, FlagMetadata? flagMetadata = null)
-        {
-            this.Value = value;
-            this.FlagKey = flagKey;
-            this.ErrorType = errorType;
-            this.Reason = reason;
-            this.Variant = variant;
-            this.ErrorMessage = errorMessage;
-            this.FlagMetadata = flagMetadata;
+                /// <summary>
+                /// Initializes a new instance of the <see cref="FlagEvaluationDetails{T}"/> class.
+                /// </summary>
+                /// <param name="flagKey">Feature flag key</param>
+                /// <param name="value">Evaluated value</param>
+                /// <param name="errorType">Error</param>
+                /// <param name="reason">Reason</param>
+                /// <param name="variant">Variant</param>
+                /// <param name="errorMessage">Error message</param>
+                /// <param name="flagMetadata">Flag metadata</param>
+                public FlagEvaluationDetails(string flagKey, T value, ErrorType errorType, string? reason, string? variant,
+                    string? errorMessage = null, ImmutableMetadata? flagMetadata = null)
+                {
+                        this.Value = value;
+                        this.FlagKey = flagKey;
+                        this.ErrorType = errorType;
+                        this.Reason = reason;
+                        this.Variant = variant;
+                        this.ErrorMessage = errorMessage;
+                        this.FlagMetadata = flagMetadata;
+                }
         }
-    }
 }

src/OpenFeature/Model/BaseMetadata.cs → src/OpenFeature/Model/ImmutableMetadata.cs

@@ -1,16 +1,31 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 
+#nullable enable
 namespace OpenFeature.Model;
 
 /// <summary>
-/// Represents the base class for metadata objects.
+/// Represents immutable metadata associated with feature flags and events.
 /// </summary>
-public abstract class BaseMetadata
+/// <seealso href="https://github.com/open-feature/spec/blob/v0.7.0/specification/types.md#flag-metadata"/>
+/// <seealso href="https://github.com/open-feature/spec/blob/v0.7.0/specification/types.md#event-metadata"/>
+public sealed class ImmutableMetadata
 {
     private readonly ImmutableDictionary<string, object> _metadata;
 
-    internal BaseMetadata(Dictionary<string, object> metadata)
+    /// <summary>
+    /// Constructor for the <see cref="ImmutableMetadata"/> class.
+    /// </summary>
+    public ImmutableMetadata()
+    {
+        this._metadata = ImmutableDictionary<string, object>.Empty;
+    }
+
+    /// <summary>
+    /// Constructor for the <see cref="ImmutableMetadata"/> class.
+    /// </summary>
+    /// <param name="metadata">The dictionary containing the metadata.</param>
+    public ImmutableMetadata(Dictionary<string, object> metadata)
     {
         this._metadata = metadata.ToImmutableDictionary();
     }
@@ -20,7 +35,7 @@ internal BaseMetadata(Dictionary<string, object> metadata)
     /// </summary>
     /// <param name="key">The key of the value to retrieve.</param>
     /// <returns>The boolean value associated with the key, or null if the key is not found.</returns>
-    public virtual bool? GetBool(string key)
+    public bool? GetBool(string key)
     {
         return this.GetValue<bool>(key);
     }
@@ -30,7 +45,7 @@ internal BaseMetadata(Dictionary<string, object> metadata)
     /// </summary>
     /// <param name="key">The key of the value to retrieve.</param>
     /// <returns>The integer value associated with the key, or null if the key is not found.</returns>
-    public virtual int? GetInt(string key)
+    public int? GetInt(string key)
     {
         return this.GetValue<int>(key);
     }
@@ -40,7 +55,7 @@ internal BaseMetadata(Dictionary<string, object> metadata)
     /// </summary>
     /// <param name="key">The key of the value to retrieve.</param>
     /// <returns>The double value associated with the key, or null if the key is not found.</returns>
-    public virtual double? GetDouble(string key)
+    public double? GetDouble(string key)
     {
         return this.GetValue<double>(key);
     }
@@ -50,7 +65,7 @@ internal BaseMetadata(Dictionary<string, object> metadata)
     /// </summary>
     /// <param name="key">The key of the value to retrieve.</param>
     /// <returns>The string value associated with the key, or null if the key is not found.</returns>
-    public virtual string? GetString(string key)
+    public string? GetString(string key)
     {
         var hasValue = this._metadata.TryGetValue(key, out var value);
         if (!hasValue)

src/OpenFeature/Model/ProviderEvents.cs

@@ -3,40 +3,39 @@
 
 namespace OpenFeature.Model
 {
-    /// <summary>
-    /// The EventHandlerDelegate is an implementation of an Event Handler
-    /// </summary>
-    public delegate void EventHandlerDelegate(ProviderEventPayload? eventDetails);
-
-    /// <summary>
-    /// Contains the payload of an OpenFeature Event.
-    /// </summary>
-    public class ProviderEventPayload
-    {
         /// <summary>
-        /// Name of the provider.
+        /// The EventHandlerDelegate is an implementation of an Event Handler
         /// </summary>
-        public string? ProviderName { get; set; }
+        public delegate void EventHandlerDelegate(ProviderEventPayload? eventDetails);
 
         /// <summary>
-        /// Type of the event
+        /// Contains the payload of an OpenFeature Event.
         /// </summary>
-        public ProviderEventTypes Type { get; set; }
+        public class ProviderEventPayload
+        {
+                /// <summary>
+                /// Name of the provider.
+                /// </summary>
+                public string? ProviderName { get; set; }
 
-        /// <summary>
-        /// A message providing more information about the event.
-        /// </summary>
-        public string? Message { get; set; }
+                /// <summary>
+                /// Type of the event
+                /// </summary>
+                public ProviderEventTypes Type { get; set; }
 
-        /// <summary>
-        /// A List of flags that have been changed.
-        /// </summary>
-        public List<string>? FlagsChanged { get; set; }
+                /// <summary>
+                /// A message providing more information about the event.
+                /// </summary>
+                public string? Message { get; set; }
 
-        /// <summary>
-        /// Metadata information for the event.
-        /// </summary>
-        // TODO: This needs to be changed to a EventMetadata object
-        public Dictionary<string, object>? EventMetadata { get; set; }
-    }
+                /// <summary>
+                /// A List of flags that have been changed.
+                /// </summary>
+                public List<string>? FlagsChanged { get; set; }
+
+                /// <summary>
+                /// Metadata information for the event.
+                /// </summary>
+                public ImmutableMetadata? EventMetadata { get; set; }
+        }
 }