C# generic types

Question

I use in my library three classes:

public abstract class Base<TFirst, TSecond>
{
    public Base()
    {
      // actions with ID and Data of TFirst and TSecond
    }
}

public abstract class First<TFirstID, TFirstData>
{
    public TFirstID ID {get; set;}
    public TFirstData Data {get; set;}
}

public abstract class Second<TSecondID, TSecondData>
{
    public TSecondID ID {get; set;}
    public TSecondData Data {get; set;}
}

How can I specify that TFirst must inherit from the First and TSecond must inherit from the Second, not using generic types for ID and Data in Base?

Like this:

public abstract class Base<TFirst, TSecond>
    where TFirst : First // without generic-types
...

Edit: In classes First, Second I use TFirstID and TSecondID for properties. In class Base I use this properties.

Answer 1

There's no way you can do this other than by introducing a parallel class hierarchy without geherics and doing some runtime checks:

public abstract class Base<TFirst, TSecond>
    where TFirst : First
{
    static Base()
    {
        if(!typeof(TFirst).IsGenericType || 
            typeof(TFirst).GetGenericTypeDefinition() != typeof(First<,>))
            throw new ArgumentException("TFirst");
    }
}

public abstract class First { }
public abstract class First<TFirstID, TFirstData> : First
{
}

Alternatively, you can replace First with a marker interface (IFirst).

The runtime check is possible due to the fact that static constructors are invoked for each closed generic type.