• Max Samuha (38/38) Jun 16 2006 Can interfaces be used as AA keys? The following code causes access
• Bruno Medeiros (21/69) Jun 18 2006 It's a bug for sure, regardless of whether interfaces can be used as AA
• BCS (17/34) Jun 19 2006 How about using an IndexForAA interface and a mixin template to pull up

Max Samuha <maxter i.com.ua_spamless> writes:

Can interfaces be used as AA keys? The following code causes access
violation (WinXP, dmd 0.160):

interface I
{
	void method();
}

class A : I
{
	void method()
	{
	}
}

void main()
{
	I a = new A();
	
	int[I] array;

	array[a] = 5; // Access violation	
}

When I replace the interface with a base class, it works.

abstract class I
{
	void method();
}

class A : I
{
	override void method()
	{
	}
}

void main()
{
	I a = new A();
	
	int[I] array;

	array[a] = 5; // Ok	
}

Is it a known bug?

Bruno Medeiros <brunodomedeirosATgmail SPAM.com> writes:

Max Samuha wrote:
 Can interfaces be used as AA keys? The following code causes access
 violation (WinXP, dmd 0.160):
 
 interface I
 {
 	void method();
 }
 
 class A : I
 {
 	void method()
 	{
 	}
 }
 
 void main()
 {
 	I a = new A();
 	
 	int[I] array;
 
 	array[a] = 5; // Access violation	
 }
 
 When I replace the interface with a base class, it works.
 
 abstract class I
 {
 	void method();
 }
 
 class A : I
 {
 	override void method()
 	{
 	}
 }
 
 void main()
 {
 	I a = new A();
 	
 	int[I] array;
 
 	array[a] = 5; // Ok	
 }
 
 Is it a known bug?

It's a bug for sure, regardless of whether interfaces can be used as AA 
keys. (If it is allowed, then the program shouldn't crash, if it isn't 
allowed the program shouldn't compile)

If it is known, I dunno, it's just a matter of searching the bugzilla.

----

Now, whether interfaces can be used as AA keys or not, it depends if we 
have a method to do hash from an interface. One way would be to require 
the interface to have a toHash method. But I'm not sure if that would 
make much sense.
Another way, perhaps the most sensible, would be to cast to Object and 
use the underlying toHash(). But that depends on whether it is allowed 
that an interface can be converted to a reference to it's underlying class.
The doc only says "A class that implements an interface can be converted 
to a reference to that interface.", but not the otherwise. However it 
seems that DMD does allow for an interface to be converted to a class 
(since that feature is what allows interface->class return type 
covariance to work), but that is all very not explicit and not documented.




-- 
Bruno Medeiros - CS/E student
http://www.prowiki.org/wiki4d/wiki.cgi?BrunoMedeiros#D

BCS <BCS pathlink.com> writes:

Bruno Medeiros wrote:
[...]
 
 Now, whether interfaces can be used as AA keys or not, it depends if we 
 have a method to do hash from an interface. One way would be to require 
 the interface to have a toHash method. But I'm not sure if that would 
 make much sense.
 Another way, perhaps the most sensible, would be to cast to Object and 
 use the underlying toHash(). But that depends on whether it is allowed 
 that an interface can be converted to a reference to it's underlying class.
 The doc only says "A class that implements an interface can be converted 
 to a reference to that interface.", but not the otherwise. However it 
 seems that DMD does allow for an interface to be converted to a class 
 (since that feature is what allows interface->class return type 
 covariance to work), but that is all very not explicit and not documented.
 
 
 
 

How about using an IndexForAA interface and a mixin template to pull up 
the right symbols. Then all that would be need would be to have the 
interface inherent that interface and away you go.


// i'm working from memory here so

interface KeyForAA
{
	uint toHash();
	int opCmp(KeyForAA);
}

template KeyForAA_Mixin
{
		// pull in the defaults from Object or the super class
	alias toHash toHash;
	alias opCmp opCmp;
}