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digitalmars.D.bugs - Classes don't inherit opIndex(Assign)

reply =?ISO-8859-1?Q?Jari-Matti_M=E4kel=E4?= <jmjmak invalid_utu.fi> writes:
Tried to make a class with multiple opIndex-structures. It only works 
when you overload the operator with the same number of arguments or 
don't use inheritance.

Here's some example code:

class A { int opIndex(int a) { return a; } }
class B:A { int opIndex(int a, int b) { return a+b; } }

void main() {
	B b = new B();
	assert(b[2] == 2);
	assert(b[2,4] == 6);
}

BTW, would it be easy to make the latter opIndex support the more common 
array syntax (ie. b[2][4])? It would certainly make the transition 
between arrays and classes a lot smoother, just like with public members 
and properties.
Sep 08 2005
parent reply "Ben Hinkle" <ben.hinkle gmail.com> writes:
"Jari-Matti Mäkelä" <jmjmak invalid_utu.fi> wrote in message 
news:dfpkqr$2ub2$1 digitaldaemon.com...

 Tried to make a class with multiple opIndex-structures. It only works when 
 you overload the operator with the same number of arguments or don't use 
 inheritance.

 Here's some example code:

 class A { int opIndex(int a) { return a; } }
 class B:A { int opIndex(int a, int b) { return a+b; } }

 void main() {
 B b = new B();
 assert(b[2] == 2);
 assert(b[2,4] == 6);
 }


That is by design. Superclass methods do not participate in overloading by 
default. It works as you expect if you instead write B as
class B:A {
  alias A.opIndex opIndex;
  int opIndex(int a, int b) { return a+b; }
}
using aliases to explicitly say that A's opIndex overloads B's opIndex.


 BTW, would it be easy to make the latter opIndex support the more common 
 array syntax (ie. b[2][4])? It would certainly make the transition between 
 arrays and classes a lot smoother, just like with public members and 
 properties.
Sep 08 2005
parent =?ISO-8859-1?Q?Jari-Matti_M=E4kel=E4?= <jmjmak invalid_utu.fi> writes:
Ben Hinkle wrote:

 "Jari-Matti Mäkelä" <jmjmak invalid_utu.fi> wrote in message 
 news:dfpkqr$2ub2$1 digitaldaemon.com...
 

Tried to make a class with multiple opIndex-structures. It only works when 
you overload the operator with the same number of arguments or don't use 
inheritance.

Here's some example code:

class A { int opIndex(int a) { return a; } }
class B:A { int opIndex(int a, int b) { return a+b; } }

void main() {
B b = new B();
assert(b[2] == 2);
assert(b[2,4] == 6);
}


 
 
 That is by design. Superclass methods do not participate in overloading by 
 default. It works as you expect if you instead write B as
 class B:A {
   alias A.opIndex opIndex;
   int opIndex(int a, int b) { return a+b; }
 }
 using aliases to explicitly say that A's opIndex overloads B's opIndex.


Thanks Ben, now I got it. I think it should be stated more clearly in 
the specs (http://www.digitalmars.com/d/function.html) that this 
behaviour includes all kinds of overloaded functions with the same name 
(not just functions with the same amount of arguments). I though these 
were somehow more "separate".
Sep 08 2005