Merge pull request #417 from RogueException/feature/better-di

Enhance Dependency Injection

src/Discord.Net.Commands/Dependencies/DependencyMap.cs

@@ -5,27 +5,59 @@ namespace Discord.Commands
 {
     public class DependencyMap : IDependencyMap
     {
-        private Dictionary<Type, object> map;
+        private Dictionary<Type, Func<object>> map;
 
         public static DependencyMap Empty => new DependencyMap();
 
         public DependencyMap()
         {
-            map = new Dictionary<Type, object>();
+            map = new Dictionary<Type, Func<object>>();
         }
 
-        public void Add<T>(T obj)
+        /// <inheritdoc />
+        public void Add<T>(T obj) where T : class 
+            => AddFactory(() => obj);
+        /// <inheritdoc />
+        public bool TryAdd<T>(T obj) where T : class
+            => TryAddFactory(() => obj);
+        /// <inheritdoc />
+        public void AddTransient<T>() where T : class, new() 
+            => AddFactory(() => new T());
+        /// <inheritdoc />
+        public bool TryAddTransient<T>() where T : class, new()
+            => TryAddFactory(() => new T());
+        /// <inheritdoc />
+        public void AddTransient<TKey, TImpl>() where TKey : class 
+            where TImpl : class, TKey, new() 
+            => AddFactory<TKey>(() => new TImpl());
+        public bool TryAddTransient<TKey, TImpl>() where TKey : class
+            where TImpl : class, TKey, new()
+            => TryAddFactory<TKey>(() => new TImpl());
+        
+        /// <inheritdoc />
+        public void AddFactory<T>(Func<T> factory) where T : class
         {
             var t = typeof(T);
             if (map.ContainsKey(t))
                 throw new InvalidOperationException($"The dependency map already contains \"{t.FullName}\"");
-            map.Add(t, obj);
+            map.Add(t, factory);
+        }
+        /// <inheritdoc />
+        public bool TryAddFactory<T>(Func<T> factory) where T : class
+        {
+            var t = typeof(T);
+            if (map.ContainsKey(t))
+                return false;
+            map.Add(t, factory);
+            return true;
         }
 
+        /// <inheritdoc />
         public T Get<T>()
         {
             return (T)Get(typeof(T));
         }
+        /// <inheritdoc />
         public object Get(Type t)
         {
             object result;
@@ -35,6 +67,7 @@ namespace Discord.Commands
                 return result;
         }
 
+        /// <inheritdoc />
         public bool TryGet<T>(out T result)
         {
             object untypedResult;
@@ -49,9 +82,17 @@ namespace Discord.Commands
                 return false;
             }
         }
+        /// <inheritdoc />
         public bool TryGet(Type t, out object result)
         {
-            return map.TryGetValue(t, out result);
+            Func<object> func;
+            if (map.TryGetValue(t, out func))
+            {
+                result = func();
+                return true;
+            }
+            result = null;
+            return false;
         }
     }
 }

src/Discord.Net.Commands/Dependencies/IDependencyMap.cs

@@ -4,12 +4,86 @@ namespace Discord.Commands
 {
     public interface IDependencyMap
     {
-        void Add<T>(T obj);
+        /// <summary>
+        /// Add an instance of a service to be injected.
+        /// </summary>
+        /// <typeparam name="T">The type of service.</typeparam>
+        /// <param name="obj">The instance of a service.</param>
+        void Add<T>(T obj) where T : class;
+        /// <summary>
+        /// Tries to add an instance of a service to be injected.
+        /// </summary>
+        /// <typeparam name="T">The type of service.</typeparam>
+        /// <param name="obj">The instance of a service.</param>
+        /// <returns>A bool, indicating if the service was successfully added to the DependencyMap.</returns>
+        bool TryAdd<T>(T obj) where T : class;
+        /// <summary>
+        /// Add a service that will be injected by a new instance every time.
+        /// </summary>
+        /// <typeparam name="T">The type of instance to inject.</typeparam>
+        void AddTransient<T>() where T : class, new();
+        /// <summary>
+        /// Tries to add a service that will be injected by a new instance every time.
+        /// </summary>
+        /// <typeparam name="T">The type of instance to inject.</typeparam>
+        /// <returns>A bool, indicating if the service was successfully added to the DependencyMap.</returns>
+        bool TryAddTransient<T>() where T : class, new();
+        /// <summary>
+        /// Add a service that will be injected by a new instance every time.
+        /// </summary>
+        /// <typeparam name="TKey">The type to look for when injecting.</typeparam>
+        /// <typeparam name="TImpl">The type to inject when injecting.</typeparam>
+        /// <example>
+        /// map.AddTransient&#60;IService, Service&#62;
+        /// </example>
+        void AddTransient<TKey, TImpl>() where TKey: class where TImpl : class, TKey, new();
+        /// <summary>
+        /// Tries to add a service that will be injected by a new instance every time.
+        /// </summary>
+        /// <typeparam name="TKey">The type to look for when injecting.</typeparam>
+        /// <typeparam name="TImpl">The type to inject when injecting.</typeparam>
+        /// <returns>A bool, indicating if the service was successfully added to the DependencyMap.</returns>
+        bool TryAddTransient<TKey, TImpl>() where TKey : class where TImpl : class, TKey, new();
+        /// <summary>
+        /// Add a service that will be injected by a factory.
+        /// </summary>
+        /// <typeparam name="T">The type to look for when injecting.</typeparam>
+        /// <param name="factory">The factory that returns a type of this service.</param>
+        void AddFactory<T>(Func<T> factory) where T : class;
+        /// <summary>
+        /// Tries to add a service that will be injected by a factory.
+        /// </summary>
+        /// <typeparam name="T">The type to look for when injecting.</typeparam>
+        /// <param name="factory">The factory that returns a type of this service.</param>
+        /// <returns>A bool, indicating if the service was successfully added to the DependencyMap.</returns>
+        bool TryAddFactory<T>(Func<T> factory) where T : class;
 
+        /// <summary>
+        /// Pull an object from the map.
+        /// </summary>
+        /// <typeparam name="T">The type of service.</typeparam>
+        /// <returns>An instance of this service.</returns>
         T Get<T>();
+        /// <summary>
+        /// Try to pull an object from the map.
+        /// </summary>
+        /// <typeparam name="T">The type of service.</typeparam>
+        /// <param name="result">The instance of this service.</param>
+        /// <returns>Whether or not this object could be found in the map.</returns>
         bool TryGet<T>(out T result);
 
+        /// <summary>
+        /// Pull an object from the map.
+        /// </summary>
+        /// <param name="t">The type of service.</param>
+        /// <returns>An instance of this service.</returns>
         object Get(Type t);
+        /// <summary>
+        /// Try to pull an object from the map.
+        /// </summary>
+        /// <param name="t">The type of service.</param>
+        /// <param name="result">An instance of this service.</param>
+        /// <returns>Whether or not this object could be found in the map.</returns>
         bool TryGet(Type t, out object result);
     }
 }

src/Discord.Net.Commands/Utilities/ReflectionUtils.cs

@@ -42,7 +42,8 @@ namespace Discord.Commands
 
                 try
                 {
-                    return (T)constructor.Invoke(args);
+                    T instance = (T)constructor.Invoke(args);
+                    return instance;
                 }
                 catch (Exception ex)
                 {