Adds ActivatorUtilities.CreateFactory<T> API (#77185)

src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/ref/Microsoft.Extensions.DependencyInjection.Abstractions.cs

@@ -9,6 +9,7 @@ namespace Microsoft.Extensions.DependencyInjection
     public static partial class ActivatorUtilities
     {
         public static Microsoft.Extensions.DependencyInjection.ObjectFactory CreateFactory([System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] System.Type instanceType, System.Type[] argumentTypes) { throw null; }
+        public static Microsoft.Extensions.DependencyInjection.ObjectFactory<T> CreateFactory<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] T>(System.Type[] argumentTypes) { throw null; }
         public static object CreateInstance(System.IServiceProvider provider, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] System.Type instanceType, params object[] parameters) { throw null; }
         public static T CreateInstance<[System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] T>(System.IServiceProvider provider, params object[] parameters) { throw null; }
         public static object GetServiceOrCreateInstance(System.IServiceProvider provider, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] System.Type type) { throw null; }
@@ -53,6 +54,7 @@ public partial interface ISupportRequiredService
         object GetRequiredService(System.Type serviceType);
     }
     public delegate object ObjectFactory(System.IServiceProvider serviceProvider, object?[]? arguments);
+    public delegate T ObjectFactory<T>(System.IServiceProvider serviceProvider, object?[]? arguments);
     public partial class ServiceCollection : Microsoft.Extensions.DependencyInjection.IServiceCollection, System.Collections.Generic.ICollection<Microsoft.Extensions.DependencyInjection.ServiceDescriptor>, System.Collections.Generic.IEnumerable<Microsoft.Extensions.DependencyInjection.ServiceDescriptor>, System.Collections.Generic.IList<Microsoft.Extensions.DependencyInjection.ServiceDescriptor>, System.Collections.IEnumerable
     {
         public ServiceCollection() { }

src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ActivatorUtilities.cs

@@ -127,11 +127,7 @@ public static ObjectFactory CreateFactory(
             [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType,
             Type[] argumentTypes)
         {
-            FindApplicableConstructor(instanceType, argumentTypes, out ConstructorInfo constructor, out int?[] parameterMap);
-
-            ParameterExpression? provider = Expression.Parameter(typeof(IServiceProvider), "provider");
-            ParameterExpression? argumentArray = Expression.Parameter(typeof(object[]), "argumentArray");
-            Expression? factoryExpressionBody = BuildFactoryExpression(constructor, parameterMap, provider, argumentArray);
+            CreateFactoryInternal(instanceType, argumentTypes, out ParameterExpression provider, out ParameterExpression argumentArray, out Expression factoryExpressionBody);
 
             var factoryLambda = Expression.Lambda<Func<IServiceProvider, object?[]?, object>>(
                 factoryExpressionBody, provider, argumentArray);
@@ -140,6 +136,40 @@ public static ObjectFactory CreateFactory(
             return result.Invoke;
         }
 
+        /// <summary>
+        /// Create a delegate that will instantiate a type with constructor arguments provided directly
+        /// and/or from an <see cref="IServiceProvider"/>.
+        /// </summary>
+        /// <typeparam name="T">The type to activate</typeparam>
+        /// <param name="argumentTypes">
+        /// The types of objects, in order, that will be passed to the returned function as its second parameter
+        /// </param>
+        /// <returns>
+        /// A factory that will instantiate type T using an <see cref="IServiceProvider"/>
+        /// and an argument array containing objects matching the types defined in argumentTypes
+        /// </returns>
+        public static ObjectFactory<T>
+            CreateFactory<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] T>(
+                Type[] argumentTypes)
+        {
+            CreateFactoryInternal(typeof(T), argumentTypes, out ParameterExpression provider, out ParameterExpression argumentArray, out Expression factoryExpressionBody);
+
+            var factoryLambda = Expression.Lambda<Func<IServiceProvider, object?[]?, T>>(
+                factoryExpressionBody, provider, argumentArray);
+
+            Func<IServiceProvider, object?[]?, T>? result = factoryLambda.Compile();
+            return result.Invoke;
+        }
+
+        private static void CreateFactoryInternal([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type instanceType, Type[] argumentTypes, out ParameterExpression provider, out ParameterExpression argumentArray, out Expression factoryExpressionBody)
+        {
+            FindApplicableConstructor(instanceType, argumentTypes, out ConstructorInfo constructor, out int?[] parameterMap);
+
+            provider = Expression.Parameter(typeof(IServiceProvider), "provider");
+            argumentArray = Expression.Parameter(typeof(object[]), "argumentArray");
+            factoryExpressionBody = BuildFactoryExpression(constructor, parameterMap, provider, argumentArray);
+        }
+
         /// <summary>
         /// Instantiate a type with constructor arguments provided directly and/or from an <see cref="IServiceProvider"/>.
         /// </summary>

src/libraries/Microsoft.Extensions.DependencyInjection.Abstractions/src/ObjectFactoryT.cs

@@ -0,0 +1,16 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+
+namespace Microsoft.Extensions.DependencyInjection
+{
+    /// <summary>
+    /// The result of <see cref="ActivatorUtilities.CreateFactory{T}"/>. A delegate to specify a factory method to call to instantiate an instance of type `T`
+    /// </summary>
+    /// <typeparam name="T">The type of the instance being returned</typeparam>
+    /// <param name="serviceProvider">The <see cref="IServiceProvider"/> to get service arguments from.</param>
+    /// <param name="arguments">Additional constructor arguments.</param>
+    /// <returns>An instance of T</returns>
+    public delegate T ObjectFactory<T>(IServiceProvider serviceProvider, object?[]? arguments);
+}

src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ActivatorUtilitiesTests.cs

@@ -170,6 +170,27 @@ public void CreateInstance_ClassWithABC_MultipleCtorsWithSameLength_ThrowsAmbigu
                 ActivatorUtilities.CreateInstance<ClassWithABC_MultipleCtorsWithSameLength>(provider));
             Assert.Equal(message, exception.Message);
         }
+
+        [Fact]
+        public void CreateFactory_CreatesFactoryMethod()
+        {
+            var factory1 = ActivatorUtilities.CreateFactory(typeof(ClassWithABCS), new Type[] { typeof(B) });
+            var factory2 = ActivatorUtilities.CreateFactory<ClassWithABCS>(new Type[] { typeof(B) });
+
+            var services = new ServiceCollection();
+            services.AddSingleton(new A());
+            services.AddSingleton(new C());
+            services.AddSingleton(new S());
+            using var provider = services.BuildServiceProvider();
+            object item1 = factory1(provider, new[] { new B() });
+            var item2 = factory2(provider, new[] { new B() });
+
+            Assert.IsType<ObjectFactory>(factory1);
+            Assert.IsType<ClassWithABCS>(item1);
+
+            Assert.IsType<ObjectFactory<ClassWithABCS>>(factory2);
+            Assert.IsType<ClassWithABCS>(item2);
+        }
     }
 
     internal class A { }