Re: Some questions on a library design

[stt@houdini.camb.inmet.com (Tucker Taft)]

Nick Roberts (Nick.Roberts@dial.pipex.com) wrote:

: Robert A Duff <bobduff@world.std.com> wrote in article
: <EBxrtu.7v6@world.std.com>...
: [...]
: > One nice thing about Ada, is that you can choose to use dispatching or
: > not, on a call-by-call basis.

: In theory, but not often in practice. 

Actually, most calls in Ada 95 end up being statically bound, whereas
in most other OOP languages, many more calls end up being dynamically
bound, even though there is no good reason for it (and oftentimes a
statically bound call would make more sense semantically as well).

: ... And in no case is the inefficiency of
: the extra tag removed, 

The extra tag imposes a small space expense, but essentially no
time overhead.  You do still have the option of creating untagged 
records in Ada 95, something not available in Java or Smalltalk.

: ... nor of the dynamic tag checking (and sometimes
: dynamic access checking).  

There are various "tag check"s in Ada, but none of them are 
performed on a statically bound call.  

An "access check" checks for null pointers, something quite
different from a "tag check."   There is also something called
an "accessibility check" which is to prevent the creation of
potentially dangling references.

You might want to check your facts a bit...

: Nick.

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-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
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