add default value static var to Property protocol

Author: chloe-yeo

Sources/FoundationEssentials/ProgressReporter/ProgressReporter+Properties.swift

@@ -15,31 +15,43 @@ extension ProgressReporter {
     public struct Properties: Sendable {
         public var totalFileCount: TotalFileCount.Type { TotalFileCount.self }
         public struct TotalFileCount: Sendable, Property {
+            public static var defaultValue: Int { return 0 }
+            
             public typealias T = Int
         }
 
         public var completedFileCount: CompletedFileCount.Type { CompletedFileCount.self }
         public struct CompletedFileCount: Sendable, Property {
+            public static var defaultValue: Int { return 0 }
+             
             public typealias T = Int
         }
 
         public var totalByteCount: TotalByteCount.Type { TotalByteCount.self }
         public struct TotalByteCount: Sendable, Property {
+            public static var defaultValue: Int64 { return 0 }
+            
             public typealias T = Int64
         }
 
         public var completedByteCount: CompletedByteCount.Type { CompletedByteCount.self }
         public struct CompletedByteCount: Sendable, Property {
+            public static var defaultValue: Int64 { return 0 }
+            
             public typealias T = Int64
         }
 
         public var throughput: Throughput.Type { Throughput.self }
         public struct Throughput: Sendable, Property {
+            public static var defaultValue: Int64 { return 0 }
+            
             public typealias T = Int64
         }
 
         public var estimatedTimeRemaining: EstimatedTimeRemaining.Type { EstimatedTimeRemaining.self }
         public struct EstimatedTimeRemaining: Sendable, Property {
+            public static var defaultValue: Duration { return Duration.seconds(0) }
+            
             public typealias T = Duration
         }
     }

Sources/FoundationEssentials/ProgressReporter/ProgressReporter.swift

@@ -110,6 +110,8 @@ internal struct AnyMetatypeWrapper: Hashable, Equatable, Sendable {
 
         associatedtype T: Sendable
 
+        static var defaultValue: T { get }
+        
         /// Aggregates an array of `T` into a single value `T`.
         /// - Parameter all: Array of `T` to be aggregated.
         /// - Returns: A new instance of `T`.
@@ -166,9 +168,13 @@ internal struct AnyMetatypeWrapper: Hashable, Equatable, Sendable {
         }
 
         /// Returns a property value that a key path indicates.
-        public subscript<P: Property>(dynamicMember key: KeyPath<ProgressReporter.Properties, P.Type>) -> P.T? {
+        public subscript<P: Property>(dynamicMember key: KeyPath<ProgressReporter.Properties, P.Type>) -> P.T {
             get {
-                state.otherProperties[AnyMetatypeWrapper(metatype: P.self)] as? P.T
+                if let val = state.otherProperties[AnyMetatypeWrapper(metatype: P.self)] as? P.T {
+                    return val
+                } else {
+                    return P.Type.defaultValue
+                }
             }
 
             set {