Interface and casting

[anon]

How can I do the following....

interface iface
{
int someMethod();
}

class c1 : iface
{
int someMethod() {return 10;}
}

class c2 : iface
{
int someMethod() {return {return 20;}
}

class Test
{
int testMethod()
{
return testInterface(new c1());
}

int testInterface(iface i)
{
// in this case, returns 10
// as it stands now, i have to
// cast it to a c1, before it will
// return correct value;
return i.testMethod
}
}

Thanks

[Jon Skeet [C# MVP]]

anon <an*******@discussions.microsoft.com> wrote:

How can I do the following....

interface iface
{
int someMethod();
}

class c1 : iface
{
int someMethod() {return 10;}
}

class c2 : iface
{
int someMethod() {return {return 20;}
}

class Test
{
int testMethod()
{
return testInterface(new c1());
}

int testInterface(iface i)
{
// in this case, returns 10
// as it stands now, i have to
// cast it to a c1, before it will
// return correct value;
return i.testMethod
}
}

Firstly, please post code which will compile - the above won't compile
for various reasons, which makes it difficult to tell what you actually
want to happen. Casting i to a c1 won't help at all, as neither iface
nor c1 declare a method testMethod. The two implementations of
someMethod also need to be public.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too

[Joe Mayo]

"anon" <an*******@discussions.microsoft.com> wrote in message
news:f6****************************@phx.gbl...

How can I do the following....

interface iface
{
int someMethod();
}

class c1 : iface
{
int someMethod() {return 10;}
}

class c2 : iface
{
int someMethod() {return {return 20;}
}

class Test
{
int testMethod()
{
return testInterface(new c1());
}

int testInterface(iface i)
{
// in this case, returns 10
// as it stands now, i have to
// cast it to a c1, before it will
// return correct value;
return i.testMethod
}
}

The only thing you can do in this case is call someMethod() on i:

int testInterface(iface i)
{
return i.someMethod();
}

because testMethod is not a member of iface. If you wanted to call
testMethod you would have to add it to iface and then add it to c1 and c2.

I don't believe you would want to cast i to c1 in testInterface. That's
because as soon as you passed a c2 or other iface derived type, you would
get an InvalidCastException.

Joe
--
http://www.csharp-station.com

[Kurt Lange]

I'm sorry Joe,

I made some mistakes when i originally posted.. please
see my new post ( interface and casting (second try) )

Thanks
Kurt

-----Original Message-----
"anon" <an*******@discussions.microsoft.com> wrote in messagenews:f6****************************@phx.gbl...

How can I do the following....

interface iface
{
int someMethod();
}

class c1 : iface
{
int someMethod() {return 10;}
}

class c2 : iface
{
int someMethod() {return {return 20;}
}

class Test
{
int testMethod()
{
return testInterface(new c1());
}

int testInterface(iface i)
{
// in this case, returns 10
// as it stands now, i have to
// cast it to a c1, before it will
// return correct value;
return i.testMethod
}
}

The only thing you can do in this case is call someMethod

() on i:
int testInterface(iface i)
{
return i.someMethod();
}

because testMethod is not a member of iface. If you wanted to calltestMethod you would have to add it to iface and then add it to c1 and c2.
I don't believe you would want to cast i to c1 in testInterface. That'sbecause as soon as you passed a c2 or other iface derived type, you wouldget an InvalidCastException.

Joe
--
http://www.csharp-station.com
.