Question

I have the following three classes

public class Base
{
    string name;
}

public class Foo : Base
{
    int value;
}

public class Bar : Base
{
    double value;
}

This is what I’m attempting

Base current = null;

if (somecondition)
    current = new Foo();
else
    current = new Bar();

for (int i=0; i<5; i++)
{
    current.value = i;           
}

The problem is VS 2010 shows an error in the loop body because Base doesn’t have a property value.

Now, I could workaround this issue by this way:

Base current = null;
bool isBar = true;

if (somecondition)
{
    current = new Foo();
    isBar = false;
}
else
    current = new Bar();

for (int i=0; i<5; i++)
{
    if (isBar)
        (current as Bar).value = i;          
    else
        (current as Foo).value = i;
}

But I was hoping for a better solution because once the loop starts iterating, the type of current isn’t going to change, yet I am going to test the type and accordingly cast it for each iteration.

What would be the right way to do this?

Answer 1

After making the fields accessible (or exposing them as accessible properties instead), your options are:

• Make your base class abstract, with an abstract method or property to set the value (and possibly return it) – the problem here is that you can’t easily do that when the two types are different
• Create an interface to do the same sort of thing, and cast to the interface
• Just cast as you are now
• Use dynamic if you’re using C# 4 – just declare current as dynamic, and you can assign to current.value and the compiler will insert code to work it out at execution time
• Redesign your code / inheritance hierarchy

Personally I would at least consider the last approach – is inheritance definitely appropriate here? Do the two types for value really need to be different? Do they have the same meaning, and if so would it make sense to push the value to the base class and potentially make it generic if you need different types?