Re: C++0x - why so restrictive with new keywords ?

From: (Andre Kaufmann)
Mon, 18 Jun 2007 04:09:34 GMT
Nicolas Pavlidis wrote:

Yes you are right. The indent of my posting was why ther's a need for
override, or the =F6perator" > in the context of overriding virtual

Sorry, misinterpreted your question.

methods of some base - class. After some discusion I found out, that it
can easily happen that someone overrides a method "by accident".
Something like this can not happen if you need express that you really
want to override a virtual method of the base class.

They point with override is that you can express your intention to
override a function.
If you derive from a virtual base class and want to override a function
and simply mistype a parameter or the functions name the method will not
be overridden, though you wanted to. The downside is, if you are lucky
the compiler will warn you or better said is able to warn you, if not
you will have a runtime error, depending on how you call the function.


struct base
   virtual void foo(unsigned int z) { cout << " base " << endl; }

struct derived : public base
    virtual void foo(int z) { cout << " derived " << endl; }

void call()
   derived a;;
   return 0;

will output


Though the intention of the developer was to override the function.
It's only a simple example, but if templates are involved or more
complex functions you simply can mistype a parameter type and you can't
check if the compiler generated the code you intended to, but only by
debugging the code.

Keywords, or in this case operators are great if they make sense, I
didn't saw the reason for intorducing such a functionality in C++.

Hope my sample has changed your mind ? ;-)

 > [...]

class c
    explicit c(int a) { for (int i =0; i < a; ++i) foo(i); } overrid=



Maybe I missunderstand your Code, but in this Context c makrs a [...]

Sorry my fault. I hacked in the code, which should have as many keywords
as possible, but didn't think about mixing keywords used for
constructors with keywords used for member functions only.
Yes, in C++ you can't make a constructor virtual and therefore can't
override it. It should only be pseudo code, illustrating that using "too
much" "operators" instead of keywords would lead to more unreadable code.
So from my point of view, in C++ rather new keywords should be used,
instead of IMHO "misusing" operators as keywords.

I'm not sure what the impact would be, if such keywords would be
intorcued. My point of view is, that the >=, > - syntax is more natur=


to C++ then override and abstract.

Well, AFAIK > instead of override has been introduced only, because
there "hasn't been enough time" to introduce a keyword before the
standard has been released.
I find looking at an interface with >=; >, = 0 and so on mixed isn't
that natural for a developer to read. Currently there is only a
difference between abstract and virtual functions. Which can be clearly
separated by viewing at the interface, but if override is introduced
IMHO it will be more hard to read and to search for overridden functions
if operators are used.

I agree that it's not "a real big deal" to use > instead of override.
Though I think in C++ enough operators are used instead of keywords and
this shouldn't be continued (IMHO).

The second point is, how the compiler can distinguish bewteen old code
that overrides methods without explicitly saying that, and new code tha=


would use the new feature.

Sadly, the compiler couldn't distinguish between new and old code. So it
would have to simply continue compiling code as it has been done before.
But if the keyword override is used, it could prompt a diagnostic
message. Currently it can't.

Thats the point I think, because C++ 0x must be backward compatible wit=


C++98, so a new compiler implementing C++0x can only warn.

I don't think so. Introducing modules in C++ would be also a good chance
to add some restrictions, in fact IIRC there are already some in the
proposal - better said: must be ;-)

Best regards,

Best regards,

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