Mark S. Miller wrote:
>
>         Only useful for instance-private instance variables, in which
>         case you may as well use lexically captured per-instance state.
>
>
>     No, "friend" is shared between two classes, no way to make a
>     closure per instance extending over both constructors. Pretend the
>     module above is an IIFE.
>
>
> You're missing my point. My point is independent of whether there are 
> two classes or one in the scope of your friend declaration. For 
> simplicity let's say there's only class A.
> |this| binding only helps when a method is applied to its bound this, 
> not to an argument.
> * It does not enable an instance of A to recognize that another 
> instance of A is an A.
> * It does not avoid the storage cost of objects-as-closures, since you 
> still need a function object per method per instance.

Sorry for being unclear -- my fault for not taking the time to develop 
the example. An example would have to avoid closure pattern even coming 
to mind, since I don't think it is relevant. The general problem is 
making a non-colliding name that can be used in two disjoint scopes, on 
objects of known provenance.

/be

Mark S. Miller wrote:

> You're missing my point. My point is independent of whether there are 
> two classes or one in the scope of your friend declaration. For 
> simplicity let's say there's only class A.
> `this` binding only helps when a method is applied to its bound this, 
> not to an argument.
>
> * It does not enable an instance of A to recognize that another instance of A is an A.
> * It does not avoid the storage cost of objects-as-closures, since you still need a function object per method per instance.

Sorry for being unclear -- my fault for not taking the time to develop 
the example. An example would have to avoid closure pattern even coming 
to mind, since I don't think it is relevant. The general problem is 
making a non-colliding name that can be used in two disjoint scopes, on 
objects of known provenance.