When I try and place a delegate in an interface, like this :
public interface ITest {
double foo();
delegate void bar();
}
I get an error "delegates cannot declare types". What is it about a
delegate that makes it incompatible in an interface. I know that an
interface cannot have any implementation - is there some implementation
detail in a delegate that I don't know about? 5 29795
"delegate void bar();"
is actually a type declaration of the "bar" type, and *not* an instance
member. Perhaps you mean:
delegate void MyDelegate();
public interface ITest {
double foo();
MyDelegate bar;
}
Marc at*****@yahoo.c om wrote: When I try and place a delegate in an interface, like this :
public interface ITest { double foo(); delegate void bar(); }
I get an error "delegates cannot declare types". What is it about a delegate that makes it incompatible in an interface. I know that an interface cannot have any implementation - is there some implementation detail in a delegate that I don't know about?
You've tried to do something like:
public interface ITest
{
public class Foo
{
}
}
Declaring a delegate is declaring a type, which can't be part of an
interface. You should declare the delegate itself elsewhere - you can
have a member of the type which *uses* the delegate, but that's a
different matter.
Jon
Jon Skeet [C# MVP] wrote: at*****@yahoo.c om wrote: When I try and place a delegate in an interface, like this :
public interface ITest { double foo(); delegate void bar(); }
I get an error "delegates cannot declare types". What is it about a delegate that makes it incompatible in an interface. I know that an interface cannot have any implementation - is there some implementation detail in a delegate that I don't know about?
You've tried to do something like:
public interface ITest { public class Foo { } }
Declaring a delegate is declaring a type, which can't be part of an interface. You should declare the delegate itself elsewhere - you can have a member of the type which *uses* the delegate, but that's a different matter.
Jon
Thanks for your replies - I think my question is : is the delgate a
type because it inherits from System.Delgates , even though the delegate
itself is not instantiated? I always thought of a delegate as a
"function pointer", but it's also a class and therefore a type.
An ***instance*** of a delegate is (essentially) a function pointer;
however, starting with the word "delegate" (with a small d) here defines the
***type*** - which is primarily the method signature for the Invoke method -
i.e. in this case it takes nothing and returns nothing. If it was a large D
(Delegate) then it would be any instance. Confusing, eh?
I've amended my previous code (to compile; whoops), and added some examples:
public delegate void MyDelegate();
public interface ITest {
double foo();
MyDelegate bar {get; set;}
Delegate fred {get; set;}
}
//...
ITest somet = new TestClasss(); // that implements ITest
somet.bar = new MyDelegate(Some Method); // creates an instance of MyDelegate
with SomeMethod as the target
somet.fred = // pretty much any random delegate, but must invoke via
DynamicInvoke
//...
static void SomeMethod() {}
Note: to add confusion, in the RHS of 2.0 expressions, the word "delegate"
can signify an /anonymous/ delegate, which /is/ an instance, not a type -
e.g.
button.Click += delegate {Debug.WriteLin e("Hi");};
Marc
Hi, Thanks for your replies - I think my question is : is the delgate a type because it inherits from System.Delgates ,
Yes, of course.
even though the delegate itself is not instantiated?
The example of Jon does not instantiate nothing, just declare a type inside
an interface, which is the error you are getting
I always thought of a delegate as a "function pointer", but it's also a class and therefore a type.
In .NET all definitions are types. from enum to attributes to classes.
--
--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
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