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From: nebbe@lglsun.epfl.ch (Robb Nebbe)
Subject: Re: Ada.strings.bounded problems?
Date: 23 Jan 1995 13:37:35 GMT
Date: 1995-01-23T13:37:35+00:00	[thread overview]
Message-ID: <1995Jan23.135503@lglsun.epfl.ch> (raw)
In-Reply-To: 3frlfa$rp2@gnat.cs.nyu.edu

dewar@cs.nyu.edu (Robert Dewar) writes:
|> It is important to realize the hit on shared generics. THe design of Ada 95
|> has been carefully done to preserve the practicality of using shared
|> generics, as is currently done by at least two implementations. In particular,
|> suppose we have a simple generic with some discrete types as arguments. It
|> seems unfortunate (both in terms of implementation complexity, and in 
|> efficiency) to require all equality operations to be done with thunks.

And of course redefining equality on discrete types is a very common
programming idiom. (For all those people who can't put up with the
overhead of comparing those unused bits :-) This is a strawman. It would
have made more sense (to me) to exclude discrete types, where the
reemergence of primitive operations is much less likely to cause a
problem and provide clean semantics for record types.

What probably bothers Magnus and others is that the justifications for
not providing semantics that are consistent with tagged types are all
pragmatic. Clearly the semantics as they are defined, which allow the
reemergence of predefined equality, are not desirable (or even justifyable)
from a language design point of view; rather, they must be justified
from on implementation point of view or other pragmatic concerns such
as upwards compatability. (which are certainly legitimate)

Maybe the cost of not providing consistant semantics between tagged
and untagged record types will exceed the cost of introducing an
upward incompatability, maybe not. It is a really tough call right
now. Especially since there really isn't any data, just speculation,
to base the decision on.

Robb Nebbe



  reply	other threads:[~1995-01-23 13:37 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <TARJEIJ.95Jan11183331@ulrik.uio.no>
1995-01-12 14:24 ` Ada.strings.bounded problems? Robert Dewar
1995-01-12 15:59 ` Norman H. Cohen
1995-01-13 19:33   ` Mats Weber
     [not found] ` <EACHUS.95Jan11170317@spectre.mitre.org>
1995-01-12 18:10   ` Robert Dewar
     [not found] ` <D29L78.J9@nntpa.cb.att.com>
1995-01-12 18:16   ` Norman H. Cohen
1995-01-13 10:52     ` Tarjei Jensen
1995-01-13 19:29     ` Mats Weber
     [not found]       ` <3fduto$ta7@watnews1.watson.ibm.com>
     [not found]         ` <Mats.Weber-1701951908250001@mlma11.matrix.ch>
1995-01-18 14:27           ` Norman H. Cohen
1995-01-19 16:49             ` Mats Weber
1995-01-21  5:28               ` Robert Dewar
     [not found]             ` <1995Jan19.124412@lglsun.epfl.ch>
1995-01-19 21:59               ` Norman H. Cohen
1995-01-23 15:56                 ` Mats Weber
1995-01-24 18:49                   ` Robert A Duff
1995-01-24 19:24                   ` Robert Dewar
1995-01-25 17:26                     ` Norman H. Cohen
     [not found]                     ` <Mats.Weber-2701952307410001@mlma11.matrix.ch>
1995-01-30 14:15                       ` David Emery
1995-02-01 14:02                         ` William Brennan
1995-02-01 14:28                           ` William Brennan
1995-02-01 20:46                           ` Robert Firth
     [not found]                             ` <3gr5b4$1eq2@info4.rus.uni-stuttgart.de>
     [not found]                               ` <D3H6qD.AD6@inmet.camb.inmet.com>
1995-02-07 20:22                                 ` Norman H. Cohen
1995-02-11 15:58                                   ` David Weller
1995-02-01 21:48                           ` Mark A Biggar
     [not found]                           ` <3grvi1$jvm@gnat.cs.nyu.edu>
1995-02-08 15:22                             ` Passive tasks (was: bounded strings) Schilling J.
1995-02-10  1:51                               ` Robert Dewar
1995-01-20 17:00               ` Ada.strings.bounded problems? Robert Dewar
1995-01-18 16:23           ` Cyrille Comar
1995-01-18 17:48           ` Robert Dewar
1995-01-19  1:36           ` Keith Thompson
1995-01-19 17:53             ` Jacob Sparre Andersen
1995-01-20 11:12               ` Robb Nebbe
1995-01-20 16:03                 ` Magnus Kempe
1995-01-21 18:57                   ` Robert Dewar
1995-01-23 13:37                     ` Robb Nebbe [this message]
1995-01-24 14:38                       ` Robert Dewar
1995-01-24 19:24                       ` Tucker Taft
1995-01-25 10:25                         ` Robb Nebbe
     [not found]                         ` <Mats.Weber-2701952308000001@mlma11.matrix.ch>
1995-01-29  5:29                           ` Robert Dewar
     [not found]           ` <1995Jan18.164836.2222@nbivax.nbi.dk>
1995-01-22 18:05             ` Tucker Taft
1995-01-12 22:17   ` Robert Dewar
     [not found]     ` <D2D8DC.JvM@nntpa.cb.att.com>
     [not found]       ` <3fja22$fab@source.asset.com>
1995-01-18 18:02         ` Norman H. Cohen
1995-01-20  5:12         ` Robert Dewar
     [not found]   ` <D2J8H0.DMu@aplcenmp.apl.jhu.edu>
1995-01-18  5:01     ` Robert Dewar
1995-01-22 18:09     ` Tucker Taft
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