C＃：Func与继承类型的构造函数(C#: Func with a constructor of an inherited type)

C＃：Func与继承类型的构造函数(C#: Func with a constructor of an inherited type)

正如我们所知，你可以像这样将一个构造函数指向Func<T> ：

Func<MyObject> constructor = () => new MyObject(); var newObject = constructor();

但是有没有办法为你知道从MyObject继承的对象创建构造函数 ，但是你不知道它的确切类型？

Type inheritedObjectType = obj; // Parameter Func<MyObject> constructor = () => new MyObject(); // as inheritedObjectType var newInheritedObject = constructor; // Should now be of the inherited type

使用Activator或任何返回Object的答案不是一个选项。

编辑 ：我不知道在编译时派生类型是什么类型。 我只有一个System.Type 。

As we know you can point to a constructor as a Func<T> like this:

Func<MyObject> constructor = () => new MyObject(); var newObject = constructor();

But is there a way to make a constructor for an object you know inherits from MyObject, but you don't know its exact type?

Type inheritedObjectType = obj; // Parameter Func<MyObject> constructor = () => new MyObject(); // as inheritedObjectType var newInheritedObject = constructor; // Should now be of the inherited type

An answer with using Activator or anything returning Object is not an option.

Edit: I don't know what type the derived type is at compile time. I only have a System.Type.

最满意答案

您可以使用表达式树来构建和编译将创建派生类型的委托：

Func<TBase> CreateDelegate<TBase>(Type derived) { var ctor = derived.GetConstructor(Type.EmptyTypes); if (ctor == null) { throw new ArgumentException("D'oh! No default ctor."); } var newExpression = Expression.Lambda<Func<TBase>>( Expression.New(ctor, new Expression[0]), new ParameterExpression[0]); return newExpression.Compile(); }

你可以简单地调用它，如下所示：

Func<MyBase> create = CreateDelegate<MyBase>(typeof(Derived)); MyBase instance = create();

当您缓存该代理时，您将获得最佳性能。

You can use expression trees to build and compile a delegate that will create your derived type:

Func<TBase> CreateDelegate<TBase>(Type derived) { var ctor = derived.GetConstructor(Type.EmptyTypes); if (ctor == null) { throw new ArgumentException("D'oh! No default ctor."); } var newExpression = Expression.Lambda<Func<TBase>>( Expression.New(ctor, new Expression[0]), new ParameterExpression[0]); return newExpression.Compile(); }

You can simply call it as follows:

Func<MyBase> create = CreateDelegate<MyBase>(typeof(Derived)); MyBase instance = create();

When you cache that delegate, you will get maximum performance.