Mark Miller wrote:
> On Tue, Jul 30, 2013 at 8:36 PM, Brendan Eich <brendan at mozilla.com 
> <mailto:brendan at mozilla.com>> wrote:
>
>     Mark S. Miller wrote:
>
>         Aside from this confinement issue, all other the advantages
>         that unique symbols have over unique-ish strings seem minor to
>         me. The biggest is default non-enumerability, when we're
>         getting away (admittedly slowly) from enumerability being
>         significant anyway. IMO, if the only advantages of unique
>         symbols over unique-ish strings are these minor ones, then
>         they don't pull their weight.
>
>         However, I don't understand the confinement scenario you have
>         in mind. Can you give an example?
>
>
>     A friend field a la C++ "friend", e.g.:
>
>     module ... {
>       const friend = Symbol(); // however it's spelled
>       class A { ... }
>       class B { ... }
>     }
>
>     where fiend is used in the ... elisions but only to access
>     properties of objects known to be instanceof A or B.
>
>
> Known how?

Lots of ways, e.g., |this| in bound methods, |this| after suitable 
instanceof tests with no mutable [[Prototype]] (e.g., A and B  are 
sealed, manually in ES6 alas, but still doable).

/be

Mark Miller wrote:
> Known how?

Lots of ways, e.g., `this` in bound methods, `this` after suitable 
instanceof tests with no mutable [[Prototype]] (e.g., A and B  are 
sealed, manually in ES6 alas, but still doable).