C# generic method with inheritance and interface

Question

this is something really simple Im sure, but Im struggling to get my head around the inheritance malarky when it comes to interfacing.

Given the following classes, how do I interface the Get method in an interface specific to class Parent, without overriding the base method?

public class Base<T, T2>
{
    public T Get<T, T2>(string key)
    {
        ...
    }
}

public class Parent : Base<Type1, Type2>, IParent
{
    ...
}

Here's what I have atm, but I keep getting a "inteface member Type1 IParent.Get(string) is not implemented" error.

public interface IParent
{
    Type1 Get(string key);
}

You do not need the Get<T,T2> in the method if they are already declared in the class. — John Alexiou
– John Alexiou, Commented Jan 2, 2013 at 16:09
Thanks for all the comments, it has helped me to understand it much better. ja72, Krizz, Charles & Guvante all hit the nail on the head, but Charles' description was the most in-depth (with code examples, no less) so he gets the green tick :) — beterthanlife
– beterthanlife, Commented Jan 2, 2013 at 16:25

Krizz · Accepted Answer · 2013-01-02 16:11:45Z

5

public T Get<T, T2>(string key) will create a generic method on generic class. T and T2 will be arguments of this generic method and will have no relation to class's T and T2.

Just make it public T Get(string key).

answered Jan 2, 2013 at 16:11

Krizz

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Comments

Charles Lambert · Accepted Answer · 2013-01-02 16:14:41Z

The T Get<T,T2>(string) method of Base<T,T2> and the method Type1 Get(string) method of IParent are two different method signatures. You would need to implement both. If you wanted both implementations to use the same functionality you could do the following:

public class ParentJ : Base<Type1, Type2>, IParent {
 public Type1 Get(string key) {
    return this.Get<Type1,Type2>(key);
 }
}

However I believe that your original intent is not to parameterize the Get() method in Base<T,T2> therefore you would write Base like so:

public class Base<T,T2> {
  public T Get(string key) {
    // implementation here
  }
}

That signature would satisfy the method signature in IParent.

You only need type parameters (e.g. T and T2) on methods when the type cannot or should not be inferred by the class that contains the method.

Guvante · Accepted Answer · 2013-01-02 16:15:24Z

2

When matching methods, this signature must match exactly. One of the components of the signature is the number of generic arguments.

Your IParent interface contains a method Get with zero type arguments. Your Base class contains a method Get with two type arguments.

While it looks like Base.Get shares its type arguments, it does not, the syntax used creates two new type arguments that shadow the type arguments of the class.

The fix is to simply implement a Get method in Parent that does not have any type arguments.

answered Jan 2, 2013 at 16:15

Guvante

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Comments

John Alexiou · Accepted Answer · 2013-01-02 16:17:49Z

1

Try this. You do not override the base Get and you implement IParent.

public class Type1 { }
public class Type2 { }

public interface IParent
{
    Type1 Get(string key);
}

public class Base<T, T2> 
{
    public T Get(string key)
    {
        return default(T);
    }
}
public class Parent : Base<Type1, Type2>, IParent
{
}

answered Jan 2, 2013 at 16:17

John Alexiou

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Comments

Rashedul.Rubel · Accepted Answer · 2013-01-02 17:33:55Z

0

try by using generic IParent interface.

answered Jan 2, 2013 at 17:33

Rashedul.Rubel

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