Converting Func<> types

Question

Cannot convert type 'System.Func<int,bool>' to 'System.Func<object,bool>'

Trying to cast f2 to f1:

    Func<object, bool> f1 = x => true;
    Func<int, bool> f2 = x => true;
    f1 = (Func<object, bool>)f2;

Tried map function to solve but, this time i get

Argument 1: cannot convert from 'C' to 'A' 

exception. on tranform(a) function

    Func<int, bool> f3 = Map(f2, x => x);

    Func<C, B> Map<A, B, C>(Func<A, B> input, Func<A, C> transform)
    {
        return x => input(transform(x));
        // return x => input(transform((A)x)); not working
    }

Is there a solution?

Answer 1

This should work:

f1 = p => f2((int)p);

Naturally, however, using this f1 will produce an InvalidCastException if you pass it something that cannot be cast to an int.

It is possible to create a generic utility function to do this, provided the input type of f2 inherits from the input type of f1 (which is true in your example - int derives from object):

static Func<TOut, TR> ConvertFunc<TIn, TOut, TR>(Func<TIn, TR> func) where TIn : TOut
{
    return p => func((TIn)p);
}

Then you can use it like this:

f1 = ConvertFunc<int, object, bool>(f2);

But that's not any more concise than my first example, and I think this second approach is somewhat less readable than the first one.

---

Incidentally, it is possible to get your Map() method to compile if you put the type arguments in the right order:

static  Func<TNewIn, TOut> Map<TOrigIn, TNewIn, TOut>(Func<TOrigIn, TOut> input, 
                                                      Func<TNewIn, TOrigIn> convert)
{
    return x => input(convert(x));
}

You can call it like this:

f1 = Map(f2, (object x) => (int)x);

You need to explicitly indicate the NewIn type because there's no way for the compiler to infer it.