C#•3y ago

inherit two interface that have same properties

hi all, i have two interfaces that have member with same name inside, and i inherit these two interfaces for some reason but i can't seem to access only one of the member from an interface.. is it possible we decide which member from which interface we wanted to use?

public interface IMemo{
  public long id {get;set;}
}

public interface IStickyNote {
  public long id {get;set;}
}
public class MyNote <T> where T :IMemo, IStickyNote {
  //if i access id member here i will get ambiguity exception 
}

public interface IMemo{
  public long id {get;set;}
}

public interface IStickyNote {
  public long id {get;set;}
}
public class MyNote <T> where T :IMemo, IStickyNote {
  //if i access id member here i will get ambiguity exception 
}

24 Replies

Yawnder•3y ago

Yes it is, but I think you fundamentally don't understand what an interface is. An interface is not an implementation. An interface is a contract that says "whomever implements that interface has to expose [this thing]". Now, in your example, you said "Anything that implements IMemo has to provide an id, and anything that implements IStickyNote has to provide an id". If anything implements both, as long as it exposes an id, it matches both contracts so you're fine.

jin.fuyouOP•3y ago

so these two conditions below are incorrect, and it shouldnt work this way if i implement an interface, is that what you mean?

Anything that implements IMemo has to provide an id, and anything that implements IStickyNote has to provide an id
If anything implements both, as long as it exposes an id, it matches both contracts so you're fine.

Anything that implements IMemo has to provide an id, and anything that implements IStickyNote has to provide an id
If anything implements both, as long as it exposes an id, it matches both contracts so you're fine.

Yawnder•3y ago

No, what I wrote (and you quoted) is what it actually is.

jin.fuyouOP•3y ago

ohh so it's correct.. hmm.. but how do we resolve the ambiguity if we want to access a member but both interface have same name?

Yawnder•3y ago

Why would there be an ambiguity?

jin.fuyouOP•3y ago

foreach (T note in allNote){
  note.id = 1234; //ambiguity between IMemo.id and IStickyNote.id

}

foreach (T note in allNote){
  note.id = 1234; //ambiguity between IMemo.id and IStickyNote.id

}

im not sure but this is the exception visual studio give..

Yawnder•3y ago

New example: There is a bar. To enter the bar, you need to be 18y or more. There is a convenient store. To buy beer there, you need to be 18y or more. If you are 20y old, is there an ambiguity as to if you can enter the bar or buy beer? As long as you meet the criteria, you're good.

jin.fuyouOP•3y ago

hmm.. because i inherit from both interfaces

public class MyNote <T> where T :IMemo, IStickyNote {
 
  public void Test(){
 //if i access id member here i will get ambiguity exception 
 foreach (T note in allNote){
  note.id = 1234; //ambiguity between IMemo.id and IStickyNote.id

 }
  }
}

public class MyNote <T> where T :IMemo, IStickyNote {
 
  public void Test(){
 //if i access id member here i will get ambiguity exception 
 foreach (T note in allNote){
  note.id = 1234; //ambiguity between IMemo.id and IStickyNote.id

 }
  }
}

and both IMemo and IStickyNote have "id" member so when i try to access "id" there's this message from visual studio ->//ambiguity between IMemo.id and IStickyNote.id

MODiX•3y ago

Yawnder#7904

REPL Result: Success

interface IA { int MyInt { get; set ; } }
interface IB { int MyInt { get; set ; } }
class C : IA, IB { public int MyInt { get; set ; } }

var c = new C();
c.MyInt = 3;
Console.WriteLine(c.MyInt);

interface IA { int MyInt { get; set ; } }
interface IB { int MyInt { get; set ; } }
class C : IA, IB { public int MyInt { get; set ; } }

var c = new C();
c.MyInt = 3;
Console.WriteLine(c.MyInt);

Console Output

Compile: 658.462ms | Execution: 58.445ms | React with ❌ to remove this embed.

Yawnder•3y ago

No, your problem is because what you wrote is non-sense an just not valid code. You can't have a foreach in a class, it needs to be in a method.

jin.fuyouOP•3y ago

ok i edited the code, i was typing in discord so there was a mistake but in the visual studio editor, the error is only in the ambiguity line

Yawnder•3y ago

Once again, it's invalid code...

jin.fuyouOP•3y ago

mm.. why..?

public class MyNote <T> where T :IMemo, IStickyNote {
 
  public void Test(){
   //if i access id member here i will get ambiguity exception 
   foreach (T note in allNote){
       note.id = 1234; //ambiguity between IMemo.id and IStickyNote.id

    }
  }
}

public class MyNote <T> where T :IMemo, IStickyNote {
 
  public void Test(){
   //if i access id member here i will get ambiguity exception 
   foreach (T note in allNote){
       note.id = 1234; //ambiguity between IMemo.id and IStickyNote.id

    }
  }
}

Yawnder•3y ago

Look, I've explained, then I've shown you with some code that compiled and executed, that it works, not sure what else I can do.

jin.fuyouOP•3y ago

ohh i should create a new object?

Yawnder•3y ago

allNote doesn't exist. It can't work.

jin.fuyouOP•3y ago

ok supposed i have this valid allNote, bcs i get the allNote from database, so i didnt post it in the code....

Thinker•3y ago

Never mind the question of why MyNote is generic in the first place

jin.fuyouOP•3y ago

yah it's a code that i take over.. i think they've some requirement on this previously.. but actually the problem is only 1, the exception only gives me "ambiguity...." from visual studio

Yawnder•3y ago

It can't say that as any and all code you've shown doesn't compile. Anyways, I'm off to bed.

Thinker•3y ago

You can't unify both interfaces with a single IHasId interface?

jin.fuyouOP•3y ago

hmm.. i saw that there'll be lots of changes.. there's solution to this from the error https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-messages/cs0229?f1url=%3FappId%3Droslyn%26k%3Dk(CS0229) - i click from the suggested link from the error but if i append ((IInterface)x).properties, it'll kind of messy..

Thinker•3y ago

I think if you just have a single IHasId interface which both IMemo and IStickyNote inherits from, then it'll work much better.

jin.fuyouOP•3y ago

i see.. alright.. i'll try to refactor the code.. thanks!

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inherit two interface that have same properties