Re: on OO differnces between Ada95 and C++

[N.Perry@massey.ac.nz (Nigel Perry)]

In article <4gt3ag$76m@druid.borland.com>, pete@borland.com (Pete Becker) wrote:

<snip>
>No, my original statement is correct: a program which contains multiple 
>definitions of the same class is not a valid C++ program because it violates 
>the one definition rule. That is exactly the case that the original message 
<snip>
>so cavalierly. There aren't many compilers that enforce this rule, but it is 
>nevertheless a constraint on valid C++ programs.

C++ Draft Standard: 3.2 One defintion rule, clause 8:

No diagnostic is required for a violation of the ODR rule.

Similarly, 3.5 Program and linkage, clause 9 ends:

A violation of this rule on type identity does not require a diagnostic

[also many other places in the Standard]

What does this mean. Well Pete may be right (I haven't checked) that the
code is "wrong", but "wrong" code does not require a diagnostic in C++.
The opposite of a diagnostic is surely a succesful compile & link (but not
necessarily a succesful execution!), so "wrong" code meets the Standard...
My guess is that defining "private" as "public" to break encapsulation
isn't forbidden by the Standard - if it was then it wouldn't be C/C++
would it? :-)

Don't people use C/C++ so they *can* break the rules? If you want strict type
checking etc. go use Ada 95, Haskell, SML, etc. etc. etc.

Just my 2c's worth :-)

-- 
Dr Nigel Perry                  Email: N.Perry@massey.ac.nz
Department of Computer Science  Tel:   +64 6 350 4007
Massey University               Fax:   +64 6 350 5611 Attn. Dr N. Perry
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