Allowing inverse registration syntax with provided instances.

Author: anaximander23

src/Lamar/InverseInstanceExpression.cs

@@ -1,38 +1,69 @@
-using System;
-using Lamar.IoC.Instances;
+using Lamar.IoC.Instances;
 using Microsoft.Extensions.DependencyInjection;
+using System;
 
 namespace Lamar
 {
     public partial class ServiceRegistry
     {
-        public class InverseInstanceExpression<TImpl> where TImpl : class
+        public class ProvidedInstanceInverseInstanceExpression<TImpl> : BaseInverseInstanceExpression<TImpl>
+            where TImpl : class
         {
-            public InverseInstanceExpression(ServiceRegistry parent)
+            public ProvidedInstanceInverseInstanceExpression(ServiceRegistry parent, TImpl instance)
+                : base(parent)
             {
-                _parent = parent;
+                _instance = instance;
             }
 
-            private readonly ServiceRegistry _parent;
+            private readonly TImpl _instance;
 
-            public ScopedInverseInstanceExpression<TImpl> Named(string name)
+            public override ScopedInverseInstanceExpression<TImpl> Named(string name)
             {
-                return new ScopedInverseInstanceExpression<TImpl>(_parent, name);
+                return new ScopedInverseInstanceExpression<TImpl>(Parent, _instance, name);
             }
 
-            public ScopedInverseInstanceExpression<TImpl> Scoped()
+            public override ScopedInverseInstanceExpression<TImpl> Singleton()
             {
-                return new ScopedInverseInstanceExpression<TImpl>(_parent, ServiceLifetime.Scoped);
+                return new ScopedInverseInstanceExpression<TImpl>(Parent, _instance);
             }
+        }
 
-            public ScopedInverseInstanceExpression<TImpl> Singleton()
+        public class InverseInstanceExpression<TImpl> : BaseInverseInstanceExpression<TImpl>
+            where TImpl : class
+        {
+            public InverseInstanceExpression(ServiceRegistry parent)
+                : base(parent)
             {
-                return new ScopedInverseInstanceExpression<TImpl>(_parent, ServiceLifetime.Singleton);
             }
 
             public ScopedInverseInstanceExpression<TImpl> Transient()
             {
-                return new ScopedInverseInstanceExpression<TImpl>(_parent, ServiceLifetime.Transient);
+                return new ScopedInverseInstanceExpression<TImpl>(Parent, ServiceLifetime.Transient);
+            }
+
+            public ScopedInverseInstanceExpression<TImpl> Scoped()
+            {
+                return new ScopedInverseInstanceExpression<TImpl>(Parent, ServiceLifetime.Scoped);
+            }
+        }
+
+        public class BaseInverseInstanceExpression<TImpl> where TImpl : class
+        {
+            public BaseInverseInstanceExpression(ServiceRegistry parent)
+            {
+                Parent = parent;
+            }
+
+            protected ServiceRegistry Parent { get; }
+
+            public virtual ScopedInverseInstanceExpression<TImpl> Named(string name)
+            {
+                return new ScopedInverseInstanceExpression<TImpl>(Parent, name);
+            }
+
+            public virtual ScopedInverseInstanceExpression<TImpl> Singleton()
+            {
+                return new ScopedInverseInstanceExpression<TImpl>(Parent, ServiceLifetime.Singleton);
             }
         }
 
@@ -50,11 +81,26 @@ public ScopedInverseInstanceExpression(ServiceRegistry parent, ServiceLifetime l
                 _lifetime = lifetime;
             }
 
-            private ServiceRegistry _parent;
+            public ScopedInverseInstanceExpression(ServiceRegistry parent, TImpl instance, string name)
+            {
+                _parent = parent;
+                _providedInstance = instance;
+                _name = name;
+            }
+
+            public ScopedInverseInstanceExpression(ServiceRegistry parent, TImpl instance)
+            {
+                _parent = parent;
+                _providedInstance = instance;
 
+                _lifetime = ServiceLifetime.Singleton;
+            }
+
+            private readonly TImpl _providedInstance;
+            private ServiceRegistry _parent;
             private string _name;
             private ServiceLifetime _lifetime;
-            private ConstructorInstance<TImpl> _rootInstance;
+            private Instance _rootInstance;
 
             public ScopedInverseInstanceExpression<TImpl> For<TService>()
                 where TService : class
@@ -87,7 +133,14 @@ private void AddRootRegistration()
             {
                 if (_rootInstance is null)
                 {
-                    _rootInstance = _parent.For<TImpl>().Use<TImpl>();
+                    if (_providedInstance is null)
+                    {
+                        _rootInstance = _parent.For<TImpl>().Use<TImpl>();
+                    }
+                    else
+                    {
+                        _rootInstance = _parent.For<TImpl>().Use(_providedInstance);
+                    }
 
                     _rootInstance.Lifetime = _lifetime;
                     if (!String.IsNullOrEmpty(_name))

src/Lamar/ServiceRegistry.cs

@@ -429,6 +429,11 @@ public InverseInstanceExpression<T> Use<T>() where T : class
         {
             return new InverseInstanceExpression<T>(this);
         }
+
+        public ProvidedInstanceInverseInstanceExpression<T> Use<T>(T instance) where T : class
+        {
+            return new ProvidedInstanceInverseInstanceExpression<T>(this, instance);
+        }
     }
 
     public enum DynamicAssemblySharing