C# Generics and Interface Inherits Interface

Question

Say I have two interfaces, IFeaturesA, IFeaturesB.

IFeaturesA has a set of signature methods. Let's say one is:-

public void printMe();

IFeaturesB implements IFeaturesA, and adds a new signature method, such as:-

public void printMeAlso();

Say I want to use a generic method, such as:-

public Check<E>(E passedItem)
{

}

If i passed in IFeaturesA, I want to be able to call the methods of this. If i pass in IFeaturesB, I want to be able to call the extra method, printMeAlso();

What is the best way to check for an interface type passed into a generic method and access its methods in C#? Is checking for the object type against the two interface types and then casting to the type the optimal way?

Aliostad · Accepted Answer · 2012-04-18 11:31:42Z

4

That does not fit the the generics.

Generics is a typeless reuse of the behaviour. If you need to check the type then it is not a good fit for generics. You may impose constraints but checking the actual type must not be done in the generic method..

All you are trying to abstract is the fact that you are passing an item. That is not an abstraction.

answered Apr 18, 2012 at 11:31

Aliostad

81.9k21 gold badges164 silver badges209 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Davos555 Over a year ago

Alright, makes sense. I wanted to cut down on having to write another method to call similar (slightly extended) functions from one of the interfaces from the other. But I guess having to write if comparison statements can be just as bloaty.

Anthony Johnston · Accepted Answer · 2012-04-18 11:36:57Z

2

use two methods

public Check(IFeaturesA passedItem) {

}

public Check(IFeaturesB passedItem) {

}

add private methods to handle commonality

answered Apr 18, 2012 at 11:36

Anthony Johnston

9,6544 gold badges49 silver badges62 bronze badges

1 Comment

Davos555 Over a year ago

Thanks for all your answers, I went with this as this was along the lines of what i was going to do initially, I just thought perhaps there was a less bloaty way of doing it, but it turns out this is just as efficient.

Tigran · Accepted Answer · 2012-04-18 11:34:24Z

1

Don't think it's a good way to achieve what you want by defining an interface, simply define classe structure, like

public class FeaturesA
{
    public virtual void printMe()
    {  
    }

}

public class FeaturesB : FeaturesA
{
    public override void printMe()
    {  
    }

}

and after use in code, like

FeaturesA a = new FeaturesA(); 
FeaturesA b = FeaturesB();
public Check(A passedItem)
{
    passedItem.printMe();
}

on Check(a) prints a, on Check(b) prints b

Hope this helps.

answered Apr 18, 2012 at 11:34

Tigran

62.3k8 gold badges90 silver badges124 bronze badges

3 Comments

Davos555 Over a year ago

I'm using the interfaces to define method signatures for a plethora of other classes - ie one has a printA functionality, the next has printA AND printB functionality, another may have printA and printB, but each class implements the method differently.

Tigran Over a year ago

@Davos555: but that doesn't change anythign from this perspective. You still have signature, you still can have (if you need) other methods, and you can use overloading, which is in case of Interfaces with Generics is not possible to achieve in a way you want it.

Davos555 Over a year ago

Thanks Tigran, was just trying to explain a bit better.

Cylon Cat · Accepted Answer · 2012-04-18 11:36:47Z

1

If you want to check the type of an item, use "is":

if (passedItem is IFeatureA) { }

If you want to constrain a generic to certain behaviors that can be defined by an interface or an abstract class, use "where":

public class foo<E> where E : IFeatureA
{
}

The latter case won't let you use IFeatureB, but any variable in the class of type E can use methods and properties defined in IFeatureA without checking type.

You might also want to look at type Dynamic, since it's closer to what you want to do.

answered Apr 18, 2012 at 11:36

Cylon Cat

7,2192 gold badges27 silver badges34 bronze badges

Comments

Tomtom · Accepted Answer · 2012-04-18 11:31:55Z

0

I would check the type of E like

if(E.GetType().Equals(typeof(IFeaturesA)){ //call method...}

answered Apr 18, 2012 at 11:31

Tomtom

9,4287 gold badges58 silver badges99 bronze badges

Comments

CodeCaster · Accepted Answer · 2012-04-18 11:34:41Z

0

This looks like a call for another interface.

If you let both interfaces inherit from IPrintable which only contains a Print() method, and extend your Check<E>(E passedItem) with where E : IPrintable, you can call passedItem.Print().

answered Apr 18, 2012 at 11:34

CodeCaster

153k24 gold badges237 silver badges287 bronze badges

Comments

Jaster · Accepted Answer · 2012-04-18 11:34:52Z

0

try the following

Check(IFeaturesA f) {}
Check(IFeaturesB f){}
Check<T>(T obj) where T : IFeaturesA, IFeaturesB {}

answered Apr 18, 2012 at 11:34

Jaster

8,6393 gold badges38 silver badges62 bronze badges

Collectives™ on Stack Overflow

C# Generics and Interface Inherits Interface

7 Answers 7

1 Comment

1 Comment

3 Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

1 Comment

1 Comment

3 Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related