Re: GNAT controlled types

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

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

: Many thanks for the comprehensive reply.  I had forgotten that the rule
: applies wholesale to tagged types (as it sensibly must).

: I have to say, with the benefit of hindsight, it might have been a better
: decision to implement controlled types in a different way.  I feel sure
: that -- by means of inlining -- undue performance penalties could be
: avoided.  It is surely inconvenient, at times, not to be able to control
: non-tagged types.  This ability may have been considered 'dangerous' or
: unnecessary by the committee, but wrongly IMHO!

Any kind of record or array may have controlled components.  I highly
recommend that you make individual components "clean up" after
themselves rather than relying on the root type being controlled.

By the way, Ada 95 was not designed by a committee.  It was designed by a 
design team, and reviewed by Ada experts throughout the international
Ada community.

The decision to base controlled types on type extension was an attempt
to ensure a relatively straightforward implementation, where the
root controlled type would contain links for inserting the controlled
object on a linked list.  Ultimately, other considerations (such as
"mutable" discriminated types) pushed us to abandon the 
links-through-the-object implementation model in our Ada 95 front end,
but I believe other compilers have taken advantage of the type
extension approach.

: Nick Roberts
: Croydon, UK

: Proprietor, ThoughtWing Software; Independent Software Development
: Consultant
: * Nick.Roberts@dial.pipex.com * Voicemail & Fax +44 181-405 1124 *

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