C#•11mo ago

✅ Interfaces in C#

Hello guys, I just learnt about interfaces, just to have an overview of what it is. From what I've understood, an interface is just a sort of "contract". That is, we say that in this particular interface, we want to have method X and property Y. Any class implementing that interface must also have method X and property Y but the way how we define the method body can be different.

I also read that "multi-inheritance" is not allowed I think in C# (just like in java I think). That's why, interfaces can be helpful because we can implement several interfaces.

Now, one thing I'm confuse about. If Class A implements interface A, if we instantiate Class A, since it's implementing interface A, it also have the "same type" as interface A? I'm asking that because I notice in an example:

C#
Person person = new Person();
DoSomething(Person)
static void DoSomething(ISomething something) {...}

C#
Person person = new Person();
DoSomething(Person)
static void DoSomething(ISomething something) {...}

Sometimes, the object person is passed as an argument to the method DoSomething while it expects the ISomething type as argument and not a person argument. But it works, why is that please.

Finally, can someone explain the use cases of interfaces and their importance please. For example if we don't create interfaces, say I have 3 classes: Animal, Dog and Cat.

What I did is, I create a "general" method in Animal, say

MakeSound

MakeSound

. Dog and Cat extends Animal so MakeSound also exist in each respective classes.

Then I would be able to override the MakeSound method just like we kind of would do in an interface. So what's the difference of implementing an interface or extending a class here please

Angius•2/4/25, 7:05 PM

Basically correct, yeah

mg•2/4/25, 7:05 PM

Sometimes, the object person is passed as an argument to the method DoSomething while it expects the ISomething type as argument and not a person argument. But it works, why is that please.

Because if

Person

Person

implements , then everything that's on is on

Person

Person

, so a

Person

Person

"is a"

FakerOP•2/4/25, 7:07 PM

yeah I see

FakerOP•2/4/25, 7:08 PM

so basically, it's the same concept of inheritance, right? Like if we have a class called "Animal" and a class call "Dog" which inherits from Animal, then, a Dog is an Animal ?

Angius•2/4/25, 7:09 PM

One example from a project I have, would be an interface, and 3-4 different implementations using different email providers.
Then, I just request an , since I don't care which service I'm currently using, I just care that I have a method

FFaker so basically, it's the same concept of inheritance, right? Like if we have a cla...

Angius•2/4/25, 7:10 PM

Sorta. I like to think of classes in terms of is, and about interfaces in terms of can

Angius•2/4/25, 7:10 PM

Say, you have your animal example. inherits and has a method. You make a , it can fly, you make a , it can fly, you make a penguin... uh-oh

Angius•2/4/25, 7:11 PM

So you use some or interface instead

AAngius Sorta. I like to think of classes in terms of *is*, and about interfaces in term...

FakerOP•2/4/25, 7:58 PM

oh ok, didn't think of it like that, that's a great way of doing it. So the idea with the Animal and Bird is that if we make Class Bird inherits Class Animal, this would mean all birds should be able to fly while this may not be true. While with interfaces, you can define sort of a template method, then define whatever implementation we want later on in case it's a penguin for example? (but then the question arise :c, if Parrot is a bird, Stork is a Bird, Penguin is a bird; they would be all categorised from the class Bird. But then this class would implement ICanFly, right? how to make that we restrict a particular bird no fly while the others fly? Using method overloading but then, can't we do that with classes?

)

Angius•2/4/25, 7:59 PM

Just implement in the birds that can fly

Angius•2/4/25, 7:59 PM

FakerOP•2/4/25, 8:00 PM

ahhh

FakerOP•2/4/25, 8:00 PM

I see

FakerOP•2/4/25, 8:00 PM

something like that

FakerOP•2/4/25, 8:00 PM

Angius•2/4/25, 8:01 PM

Yep, basically

FakerOP•2/4/25, 8:02 PM

yeah I understand now, how inheritance differs from interfaces, the idea is that, using inheritance, what Class A inherit from say Class B, Class A can do everything that B can. Using interfaces, we can restrict that though, like instead of defining a in class B, we can implement it as an interface where only specific birds will be able to fly (please correct if I'm wrong)

Angius•2/4/25, 8:03 PM

Yeah

Angius•2/4/25, 8:04 PM

And you can implement multiple interfaces per class

Angius•2/4/25, 8:04 PM

Which you cannot do with inheritance

FakerOP•2/4/25, 8:04 PM

yep noted

FakerOP•2/4/25, 8:04 PM

I now have a clearer concept, thanks !!!

Angius•2/4/25, 8:05 PM

That can be now reused on , for example. And some can be implemented both by and

Angius•2/4/25, 8:05 PM

And so on

FakerOP•2/4/25, 8:05 PM

yeah I see