Create generic Func from reflection

Question

I\'ve specified type in a variable: Type hiddenType. I need to create a Func delegate where T is of type specified in mentioned v

Answer 1

You can solve this by building an expression tree manually, and inserting a cast to hiddenType. This is allowed when you construct an expression tree.

var typeConst = Expression.Constant(hiddenType);
MethodInfo getInst = ... // <<== Use reflection here to get GetInstance info
var callGetInst = Expression.Call(getInst, typeConst);
var cast = Expression.Convert(callGetInst, hiddenType);
var del = Expression.Lambda(cast).Compile();

Note: the above code assumes that GetInstance is static. If it is not static, change the way you construct callGetInst to pass the object on which the method is invoked.

Answer 2

Instead of using a Type, you could consider using a generic wrapper, if it's not possible for you to change the GetInstance signature:

private Func<THidden> GetTypedInstance<THidden>()
{
    return () => (THidden)GetInstance(typeof(THidden));
}

Then you can just call it with

GetTypedInstance<SomeClass>();

instead of

GetInstance(typeof(SomeClass));