[cap-talk] EQ, MyCap? review (was: Toby's Confused deputy statement)

[Mark Miller]

On Feb 11, 2008 3:45 PM, Jed Donnelley <jed at nersc.gov> wrote:
> In E, for example, the "MyCap?" notion appears
> implicitly in private references.  Consider this
> implementation of makeBrandPair:
> _________
> # E sample
> def makeBrandPair(nickname) {
>      def noObject{}
>      var shared := noObject
>      def makeSealedBox(obj) {
>          def box {
>              to shareContent() {shared := obj}
>          }
>          return box
>      }
>      def sealer {
>          to seal(obj) {return makeSealedBox(obj)}
>      }
>      def unsealer {
>          to unseal(box) {
>              shared := noObject
>              box.shareContent()
>              if (shared == noObject) {throw("invalid box")}
>              def contents := shared
>              shared := noObject
>              return contents
>          }
>      }
>      return [sealer, unsealer]
> }
> ______
>
> I think the essence of MyCap? is there in the
> box.shareContent() operation which will only
> set the "shared" variable if (I assume) the
> private "shareContent" operation is available
> on the "box" parameter that was sent in to the
> unsealer.

I don't understand what this is saying, so I can't tell whether it is
accurate or not. Can you expand? Thanks.


-- 
Text by me above is hereby placed in the public domain

    Cheers,
    --MarkM