Fishery

Source/FisheryLib/SingletonFactory.cs

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+// Copyright (c) 2022 bradson
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at https://mozilla.org/MPL/2.0/.
+
+using System.Collections.Concurrent;
+
+namespace FisheryLib;
+public abstract class SingletonFactory<T_base> where T_base : notnull
+{
+	/// <summary>
+	/// Get a Singleton instance of a type derived from T_base
+	/// </summary>
+	/// <typeparam name="T">The type of the instance</typeparam>
+	/// <returns>The Singleton instance</returns>
+	public static T Get<T>() where T : T_base
+		=> (T)GetInternal(typeof(T));
+
+	/// <summary>
+	/// Get a Singleton instance of a type derived from T_base
+	/// </summary>
+	/// <param name="type">The type of the instance</param>
+	/// <returns>The Singleton instance</returns>
+	public static T_base Get(Type type)
+	{
+		if (!typeof(T_base).IsAssignableFrom(type))
+			ThrowHelper.ThrowArgumentException($"Parameters for {typeof(T_base).Name}.Get must be assignable from Type {typeof(T_base).Name}. Got {type.FullDescription()} instead.");
+
+		return GetInternal(type);
+	}
+
+	/// <summary>
+	/// protected to allow declaring of default values on derived types. Do not directly invoke this constructor or expose it as public.
+	/// </summary>
+	protected SingletonFactory()
+	{
+		if (_instances.ContainsKey(GetType()))
+			ThrowHelper.ThrowInvalidOperationException($"Tried creating a second instance of {GetType().Name}. Only the {typeof(T_base).Name}.Get method should be used for instantiation.");
+	}
+
+	private static T_base GetInternal(Type type) => _instances.GetOrAdd(type, type => (T_base)Activator.CreateInstance(type, true));
+
+	private static readonly ConcurrentDictionary<Type, T_base> _instances = new();
+}