I need to implement the method:
object GetFactory(Type type); This method needs to return a Func<T> where typeparam 'T' is the 'type'.
So, my problem is that I don't know how to create a Func<?> at runtime using reflection. Activator.CreateInstance doesn't work because there are no constructors on delegates.
Any Ideas?
You use Delegate.CreateDelegate, i.e. from a MethodInfo; below, I've hard-coded, but you would use some logic, or Expression, to get the actual creation method:
using System; using System.Reflection; class Foo {} static class Program { static Func<T> GetFactory<T>() { return (Func<T>)GetFactory(typeof(T)); } static object GetFactory(Type type) { Type funcType = typeof(Func<>).MakeGenericType(type); MethodInfo method = typeof(Program).GetMethod("CreateFoo", BindingFlags.NonPublic | BindingFlags.Static); return Delegate.CreateDelegate(funcType, method); } static Foo CreateFoo() { return new Foo(); } static void Main() { Func<Foo> factory = GetFactory<Foo>(); Foo foo = factory(); } } For non-static methods, there is an overload of Delegate.CreateDelegate that accepts the target instance.
I use this with generics in EF Core including making Expression<Func<SomeModelType,bool>> for let's say a Where clause, you can chain MakeGenericType calls with nested generics.
var someType = SomeDbContext.SomeDataModelExample.GetType(); var funcType1 = typeof(Func<>).MakeGenericType(new Type[] { someType }); var result = Activator.CreateInstance(funcType1); var result2 = Activator.CreateInstance(funcType1, someParams); I think the usual approach would be to make the "dumb" version be the thing that you spoof at runtme, and then provide a helper extension method to provide the type-safe version on top of it.
you could create Expression objects instead of a func, and compile() the expression to get a Func delegate.
