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Re: [caplet] Re: ADsafe rules

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  • Kris Zyp
    AFAIK, no implementation has ever actually done this joining , and I believe ES3.1 and ES4 will very likely dissallow joining to prevent it from ever
    Message 1 of 13 , Apr 5, 2008
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      AFAIK, no implementation has ever actually done this "joining", and I believe ES3.1 and ES4 will very likely dissallow joining to prevent it from ever happening in the future.
      Kris
       
      ----- Original Message -----
      Sent: Saturday, April 05, 2008 9:42 PM
      Subject: Re: [caplet] Re: ADsafe rules

      Function mutability can be a source of undefined behavior since the spec allows but doesn't require "joining" of functions that have the same body and scope chain, and mutations to one of a joined pair must be reflected on the other.

      JScript deviations section 3.7 says in
      function foo() {
        function bar() {}
        return bar;
      }

      var f = foo();
      var g = bar();
      f.x = 1;
      g.x = 2;

      alert(f.x + g.x);  // could legally be either 3 or 4



      On 05/04/2008, Douglas Crockford <douglas@crockford. com> wrote:

      I want .get and .set to work without blacklists. They are intended to
      get and set data members in objects. So that is all they will allow.
      They will not get or set function values. They will not manipulate
      functions. JavaScript's functions are mutable objects. I think that
      was a mistake.

      Some of the member restrictions are motivated by obvious attacks
      (apply, call, eval, prototype, watch). Some are to prevent rights
      amplification even in cases where that does not lead to known exploits
      (callee, caller, constructor, unwatch). Some are because they make me
      nervous (valueOf).


    • Mark Miller
      ... Yes, that s what we decided. ES3.1 and ES4 will be deterministic in this regard. No joining. -- Text by me above is hereby placed in the public domain
      Message 2 of 13 , Apr 6, 2008
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        On Sat, Apr 5, 2008 at 9:09 PM, Kris Zyp <kris@...> wrote:
        > AFAIK, no implementation has ever actually done this "joining", and I
        > believe ES3.1 and ES4 will very likely dissallow joining to prevent it from
        > ever happening in the future.

        Yes, that's what we decided. ES3.1 and ES4 will be deterministic in
        this regard. No joining.

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

        Cheers,
        --MarkM
      • David-Sarah Hopwood
        ... If functions were immutable, joining would be a transparent optimization. Apart from the theoretical potential for backward incompatibility, why isn t this
        Message 3 of 13 , Apr 6, 2008
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          Mark Miller wrote:
          > On Sat, Apr 5, 2008 at 9:09 PM, Kris Zyp <kris@...> wrote:
          >> AFAIK, no implementation has ever actually done this "joining", and I
          >> believe ES3.1 and ES4 will very likely dissallow joining to prevent it from
          >> ever happening in the future.
          >
          > Yes, that's what we decided. ES3.1 and ES4 will be deterministic in
          > this regard. No joining.

          If functions were immutable, joining would be a transparent optimization.
          Apart from the theoretical potential for backward incompatibility, why
          isn't this a better solution? I suspect that very few programs rely on
          mutating actual functions (as opposed to creating mutable objects that are
          callable as functions, or mutating Function.prototype).

          --
          David-Sarah Hopwood
        • David-Sarah Hopwood
          ... Actually not quite, because it would still be observable by using ===. ... -- David-Sarah Hopwood
          Message 4 of 13 , Apr 6, 2008
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            David-Sarah Hopwood wrote:
            > Mark Miller wrote:
            >> On Sat, Apr 5, 2008 at 9:09 PM, Kris Zyp <kris@...> wrote:
            >>> AFAIK, no implementation has ever actually done this "joining", and I
            >>> believe ES3.1 and ES4 will very likely dissallow joining to prevent
            >>> it from
            >>> ever happening in the future.
            >>
            >> Yes, that's what we decided. ES3.1 and ES4 will be deterministic in
            >> this regard. No joining.
            >
            > If functions were immutable, joining would be a transparent optimization.

            Actually not quite, because it would still be observable by using ===.
            But my question stands:

            > Apart from the theoretical potential for backward incompatibility, why
            > isn't this a better solution? I suspect that very few programs rely on
            > mutating actual functions (as opposed to creating mutable objects that are
            > callable as functions, or mutating Function.prototype).

            --
            David-Sarah Hopwood
          • Kris Zyp
            ... Really? It is actually even used in ADsafe s core library. Mutating functions is pretty core functionality, and AFAIK it is necessary to form multi-level
            Message 5 of 13 , Apr 6, 2008
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              > If functions were immutable, joining would be a transparent optimization.
              >
              Apart from the theoretical potential for backward incompatibility, why
              >
              isn't this a better solution? I suspect that very few programs rely on
              >
              mutating actual functions
              Really? It is actually even used in ADsafe's core library. Mutating functions is pretty core functionality, and AFAIK it is necessary to form multi-level prototypical inheritance. If I want object A to delegate/inherit from preexisting object B, I must create a function and set the prototype (a mutation) to object B and then construct with that function. See the beget function in ADsafe.
              I would extremely surprised if function mutation is less common than some of the things that the ES3.1 and ES4 groups have to maintain for backwards compatibility (the latest was being able override the Error built-in). I have used it other situations as well, like using storing a list of listeners on a AOP advising function. AOP style event listeners are common in popular JS libraries as well, and I would imagine they use such techiniques as well.
               
              > (as opposed to creating mutable objects that are
              > callable as functions, or
              mutating Function.prototype) .

              How do make a regular object callable?
               
              Kris
               
               
               
              ----- Original Message -----
              Sent: Sunday, April 06, 2008 9:17 AM
              Subject: Re: [caplet] Mutability of functions in ECMAScript

              Mark Miller wrote:
              > On Sat, Apr 5, 2008 at 9:09 PM, Kris Zyp <kris@sitepen. com> wrote:
              >> AFAIK, no implementation has ever actually done this "joining", and I
              >> believe ES3.1 and ES4 will very likely dissallow joining to prevent it from
              >> ever happening in the future.
              >
              > Yes, that's what we decided. ES3.1 and ES4 will be deterministic in
              > this regard. No joining.

              If functions were immutable, joining would be a transparent optimization.
              Apart from the theoretical potential for backward incompatibility, why
              isn't this a better solution? I suspect that very few programs rely on
              mutating actual functions (as opposed to creating mutable objects that are
              callable as functions, or mutating Function.prototype) .

              --
              David-Sarah Hopwood

            • Mike Samuel
              Does anyone know the rationale for putting joining in the spec in the first place? mike
              Message 6 of 13 , Apr 6, 2008
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                Does anyone know the rationale for putting joining in the spec in the first place?

                mike




                On 06/04/2008, Mark Miller <erights@...> wrote:

                On Sat, Apr 5, 2008 at 9:09 PM, Kris Zyp <kris@...> wrote:
                > AFAIK, no implementation has ever actually done this "joining", and I
                > believe ES3.1 and ES4 will very likely dissallow joining to prevent it from
                > ever happening in the future.

                Yes, that's what we decided. ES3.1 and ES4 will be deterministic in
                this regard. No joining.

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

                Cheers,
                --MarkM


              • David-Sarah Hopwood
                ... You re right, I don t know what I was thinking of. Making functions immutable in ES3.1/4 is not practical. -- David-Sarah Hopwood
                Message 7 of 13 , Apr 6, 2008
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                  Kris Zyp wrote:
                  >> If functions were immutable, joining would be a transparent optimization.
                  >> Apart from the theoretical potential for backward incompatibility, why
                  >> isn't this a better solution? I suspect that very few programs rely on
                  >> mutating actual functions
                  >
                  > Really? It is actually even used in ADsafe's core library. Mutating functions
                  > is pretty core functionality, and AFAIK it is necessary to form multi-level
                  > prototypical inheritance. If I want object A to delegate/inherit from
                  > preexisting object B, I must create a function and set the prototype (a
                  > mutation) to object B and then construct with that function. See the beget
                  > function in ADsafe. I would extremely surprised if function mutation is less
                  > common than some of the things that the ES3.1 and ES4 groups have to maintain
                  > for backwards compatibility (the latest was being able override the Error
                  > built-in). I have used it other situations as well, like using storing a
                  > list of listeners on a AOP advising function. AOP style event listeners are
                  > common in popular JS libraries as well, and I would imagine they use such
                  > techiniques as well.
                  >
                  >> (as opposed to creating mutable objects that are
                  >> callable as functions, or mutating Function.prototype).
                  >
                  > How do make a regular object callable?

                  You're right, I don't know what I was thinking of. Making functions
                  immutable in ES3.1/4 is not practical.

                  --
                  David-Sarah Hopwood
                • Mark S. Miller
                  ... I d guess it was to enable the optimization that David was suggesting. But I don t actually know. -- Cheers, --MarkM
                  Message 8 of 13 , Apr 6, 2008
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                    On Sun, Apr 6, 2008 at 12:30 PM, Mike Samuel <mikesamuel@...> wrote:
                    > Does anyone know the rationale for putting joining in the spec in the first
                    > place?

                    I'd guess it was to enable the optimization that David was suggesting.
                    But I don't actually know.


                    --
                    Cheers,
                    --MarkM
                  • Douglas Crockford
                    ... optimization. ... functions is pretty core functionality, and AFAIK it is necessary to form multi-level prototypical inheritance. If I want object A to
                    Message 9 of 13 , Apr 8, 2008
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                      --- In caplet@yahoogroups.com, "Kris Zyp" <kris@...> wrote:
                      > > If functions were immutable, joining would be a transparent
                      optimization.
                      > > Apart from the theoretical potential for backward incompatibility, why
                      > > isn't this a better solution? I suspect that very few programs rely on
                      > > mutating actual functions

                      > Really? It is actually even used in ADsafe's core library. Mutating
                      functions is pretty core functionality, and AFAIK it is necessary to
                      form multi-level prototypical inheritance. If I want object A to
                      delegate/inherit from preexisting object B, I must create a function
                      and set the prototype (a mutation) to object B and then construct with
                      that function. See the beget function in ADsafe.


                      beget is a workaround for the lack of an operator that produces an
                      object with a delegation relationship. It should not be interpreted as
                      proof that mutable functions are desirable.
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