From -1051624232096595737 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 109fba,109af18a94b8a35c X-Google-Attributes: gid109fba,public X-Google-Thread: f78e5,e5cae9ffbf1dd57e X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1992-10-09 15:53:56 PST Xref: sparky comp.lang.c++:14808 comp.std.c++:1367 Newsgroups: comp.lang.c++,comp.std.c++ Path: sparky!uunet!munnari.oz.au!yarrina.connect.com.au!yarra!mel.dit.csiro.au!mineng.dmpe.CSIRO.AU!dmssyd.syd.dms.CSIRO.AU!metro!extro.ucc.su.OZ.AU!maxtal From: maxtal@extro.ucc.su.OZ.AU (John MAX Skaller) Subject: Re: The concept of templates considered ill designed Message-ID: <1992Oct9.172812.3446@ucc.su.OZ.AU> Sender: news@ucc.su.OZ.AU Nntp-Posting-Host: extro.ucc.su.oz.au Organization: MAXTAL P/L C/- University Computing Centre, Sydney References: <23808@alice.att.com> <23822@alice.att.com> Date: Fri, 9 Oct 1992 17:28:12 GMT Lines: 61 In article <23822@alice.att.com> ark@alice.UUCP () writes: >In article osoelgaultier+@CMU.EDU (Stefan Monnier) writes: > >> What I say is just that inheritance constraint permits to check >> the file and compile it before using it ! > >I understand that that is what you're saying, but you haven't convinced me. > Me neither, but I haven't given up on the idea that you might just be able to compile templates. Consider template f(T *t){t->print();} The constraint is that T must have a member function 'print()'. Now it seems that you can compile this routine, but you have to replace 'print' with a pointer supplied silently as a parameter to f. The call f(pObject); is checked against the constraints, if it passes this test, f is called with the pointer pObject AND the address of its print routine. More general cases would require the addresses of constructors to be passed (i'm glossing over lots of issues here). > >My point in giving this example is to show that statements like `constraining >template types makes compile-time type checking possible' cannot be made >casually -- it is the responsibility of the person making such a statement >to provide evidence that the statement is indeed true. > >This stuff is **difficult**! Don't take it lightly! >-- > --Andrew Koenig > ark@europa.att.com So I'm not making the claim it can be done, only throwing in a suggesting of HOW it might be done. But I reject the notion that the constraints should be named base classes, rather, the constraints are the silent parameters mentioned above, they are the 'functions' that the type T must have. (Yes this is a crude description, its just an idea. Can it be made to work, if not why not, if so what we gain is type checked templates, we loose efficiency, at least: what else, and is it worth it?) BTW: the constraints of course DO form a kind of abstract, unnamed, 'base' class that you *might* have derived the type T from had you thought of it. -- ;---------------------------------------------------------------------- JOHN (MAX) SKALLER, maxtal@extro.ucc.su.oz.au Maxtal Pty Ltd, 6 MacKay St ASHFIELD, NSW 2131, AUSTRALIA ;--------------- SCIENTIFIC AND ENGINEERING SOFTWARE ------------------