feat!: Use same type for flag metadata and event metadata (#241)

## This PR

**BREAKING CHANGE**, merge with 2.0

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 ImmutableMetadata, make sealed class and
implement a empty constructor


### Related Issues

Fixes: #234

---------

Signed-off-by: Benjamin Evenson <2031163+benjiro@users.noreply.github.com>
Signed-off-by: Todd Baert <todd.baert@dynatrace.com>
Co-authored-by: Todd Baert <todd.baert@dynatrace.com>

src/OpenFeature/Model/FlagEvaluationDetails.cs

@@ -1,55 +1,55 @@
 using OpenFeature.Constant;
 
 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>
-    {
+    public sealed class FlagEvaluationDetails<T>
+    {
         /// <summary>
         /// Feature flag evaluated value
         /// </summary>
-        public T Value { get; }
-
+        public T Value { get; }
+
         /// <summary>
         /// Feature flag key
         /// </summary>
-        public string FlagKey { get; }
-
+        public string FlagKey { get; }
+
         /// <summary>
         /// Error that occurred during evaluation
         /// </summary>
-        public ErrorType ErrorType { get; }
-
+        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; }
-
+        public string? ErrorMessage { get; }
+
         /// <summary>
         /// Describes the reason for the outcome of the evaluation process
         /// </summary>
-        public string? Reason { get; }
-
+        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; }
-
+        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; }
-
+        public ImmutableMetadata? FlagMetadata { get; }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="FlagEvaluationDetails{T}"/> class.
         /// </summary>
@@ -60,16 +60,16 @@ public sealed class FlagEvaluationDetails<T>
         /// <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;
-        }
+        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

@@ -36,7 +36,6 @@ public class ProviderEventPayload
         /// <summary>
         /// Metadata information for the event.
         /// </summary>
-        // TODO: This needs to be changed to a EventMetadata object
-        public Dictionary<string, object>? EventMetadata { get; set; }
+        public ImmutableMetadata? EventMetadata { get; set; }
     }
 }

src/OpenFeature/Model/ResolutionDetails.cs

@@ -1,54 +1,54 @@
 using OpenFeature.Constant;
 
 namespace OpenFeature.Model
-{
+{
     /// <summary>
     /// Defines the contract that the <see cref="FeatureProvider"/> is required to return
     /// Describes the details of the feature flag being evaluated
     /// </summary>
     /// <typeparam name="T">Flag value type</typeparam>
     /// <seealso href="https://github.com/open-feature/spec/blob/v0.7.0/specification/types.md#resolution-details"/>
-    public sealed class ResolutionDetails<T>
-    {
+    public sealed class ResolutionDetails<T>
+    {
         /// <summary>
         /// Feature flag evaluated value
         /// </summary>
-        public T Value { get; }
-
+        public T Value { get; }
+
         /// <summary>
         /// Feature flag key
         /// </summary>
-        public string FlagKey { get; }
-
+        public string FlagKey { get; }
+
         /// <summary>
         /// Error that occurred during evaluation
         /// <see cref="ErrorType"/>
         /// </summary>
-        public ErrorType ErrorType { get; }
-
+        public ErrorType ErrorType { get; }
+
         /// <summary>
         /// Message containing additional details about an error.
         /// </summary>
-        public string? ErrorMessage { get; }
-
+        public string? ErrorMessage { get; }
+
         /// <summary>
         /// Describes the reason for the outcome of the evaluation process
         /// <see cref="Reason"/>
         /// </summary>
-        public string? Reason { get; }
-
+        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; }
-
+        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; }
-
+        public ImmutableMetadata? FlagMetadata { get; }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="ResolutionDetails{T}"/> class.
         /// </summary>
@@ -59,16 +59,16 @@ public sealed class ResolutionDetails<T>
         /// <param name="variant">Variant</param>
         /// <param name="errorMessage">Error message</param>
         /// <param name="flagMetadata">Flag metadata</param>
-        public ResolutionDetails(string flagKey, T value, ErrorType errorType = ErrorType.None, string? reason = null,
-            string? variant = null, 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;
-        }
+        public ResolutionDetails(string flagKey, T value, ErrorType errorType = ErrorType.None, string? reason = null,
+            string? variant = null, 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;
+        }
     }
 }