why we cannot use fields in interface c#

Devinder Kumar

11y937Visual Basic .NET

3 Replies

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Mukesh Kumar11y ago
Hi,
Though many of the other answers are correct at the semantic level, I find it interesting to also approach these sorts of questions from the implementation details level.
An interface can be thought of as a collection of slots, which contain methods. When a class implements an interface, the class is required to tell the runtime how to fill in all the required slots. When you say
interface IFoo { void M(); } class Foo : IFoo { public void M() { ... } }
the class says "when you create an instance of me, stuff a reference to Foo.M in the slot for IFoo.M.
Then when you do a call:
IFoo ifoo = new Foo(); ifoo.M();
the compiler generates code that says "ask the object what method is in the slot for IFoo.M, and call that method.
If an interface is a collection of slots that contain methods, then some of those slots can also contain the get and set methods of a property, the get and set methods of an indexer, and the add and remove methods of an event. But a field is not a method. There's no "slot" associated with a field that you can then "fill in" with a reference to the field location. And therefore, interfaces can define methods, properties, indexers and events, but not fields.
thanks
0
Priyaranjan K S11y ago
Hi Dev ,

Interface is like an agreement or better say Contract that asks the Class that implements the interface to define all the methods within the interface . Now methods within the interface can be defined inside the class by associating a logic for that class , but a field cannot be defined or implemented/assigned a value within the class . However value assignments can be done using Properties because they have a getter/setter method as below :

interface IEmployee
{
string Name
{
get;
set;
}
}
public class Employee : IEmployee
{
private string name;
public string Name // read-write instance property
{
get
{
return name;
}
set
{
name = value;
}
}

}

Thanks,
Priyan

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Munesh Sharma11y ago
If an interface is a collection of slots that contain methods, then some of those slots can also contain the get and set methods of a property, the get and set methods of an indexer, and the add and remove methods of an event. But a field is not a method. There's no "slot" associated with a field that you can then "fill in" with a reference to the field location. And therefore, interfaces can define methods, properties, indexers and events, but not fields.
0