Question

I have method that looks something like

ISomething<U> Foo<T, U>(Expression<Func<T, U>> selector)
{
    Expression<Func<T, object>> generalSelector =
         ChangeSelectorReturnType<object>(selector);
    Use(generalSelector);
    return new Something<U>(selector);
}

What is the simplest code to implement ChangeSelectorReturnType assuming selector will always be a simple property accessor such as x => x.Property?

I know the solution presented in another question works, but it requires a full expression visitor because no assumptions are made. I’m ok with assumptions in this case.

Answer 1

Use the Convert() expression on the body of the lambda. That will allow you to change its type. Then recreate the lambda.

var modifiedBody = Expression.Convert(selector.Body, typeof(object));
var generalSelector =
    Expression.Lambda<Func<T, object>>(modifiedBody, selector.Parameters);