Re: Ada Popularity: Comparison of Ada/Charles with C++ STL (and Perl)

[kevin.cline@gmail.com (Kevin Cline)]

Matthew Heaney <matthewjheaney@earthlink.net> wrote in message news:<uk6ukb74c.fsf@earthlink.net>...
> kevin.cline@gmail.com (Kevin Cline) writes:
> 
> > Georg Bauhaus <sb463ba@l1-hrz.uni-duisburg.de> wrote:
> > > Is the intention to first store a 0 with word, and then
> > > to increment the value stored at word?
> > 
> > My understanding is that Insert will insert a new key/value pair into
> > the map if no entry exists for the given key, and outputs the iterator
> > I pointing to the key/value pair for the given key.
> 
> Yes.  This behavior is identical to the C++ statements:
> 
>    typedef std::map<std::string, int> wcmap_t;
> 
>    wcmap_t wcmap;
> 
>    typedef wcmap_t::iterator iter_t;
>    typedef std::pair<iter_t, bool> status_t;
> 
>    const status_t status = wcmap.insert(std::make_pair(word, 0));
>    const iter_t i = status.first;
>    ++i->second;
>    
> 
> > > Although this will require that you know how to separate the queries
> > > and commands in this abbreviation. If you are not used to how ++ and
> > > [] work in the context of maps, will this still be easy to
> > > understand?
> > 
> > The only question is whether the [] operator will create an entry if
> > none exists.  Thirty seconds with the reference will confirm that it
> > does, and I would expect a professional programmer to be able to
> > remember that.
> 
> Yes, the index operator creates an element with its default value, if
> the requested key isn't already in the map.
> 
> Note, however, that the index operator isn't completely benign.  In
> fact, the index operator for map gets its own entry in Effective STL.
> 
> One thing programmers sometimes do is:
> 
>    some_map[some_key] = x;
> 
> The issue here is that the element associated with some_key gets
> constructed using its default ctor, and then the object is immediately
> assigned the value of x.  But it's more efficient to use the copy ctor,
> but to do that you need to use the insert member function as above.
> 
> The other issue with the index operator is that if you use a (string)
> literal as the key, then it's possible to misspell the value, and create
> a new key accidently.
> 
> That being said, for this particular problem, the index operator is very
> convenient, and entirely appropriate.
> 
>    
> > > AFAIK, [] does more than one thing behind the scenes.  
> > > ++ is known to be difficult to understand in that it
> > > is not clear what ++ is referring to. 
> > 
> > Now are you claiming that C++ is hard to read because one has to learn
> > the operator precedence rules?
> 
> The rule in C and C++ is that postfix operators have a higher precedence
> than prefix operators.  This is the only rule that makes sense, for
> example:
> 
>    struct S { int i; };
> 
>    S s = { 0 };
> 
>    ++s.i;
> 
> In this case, the operator is the "dot" operator (which isn't
> user-definable).
> 
> Actually, I would have used a pointer instead:
> 
>    S* ps = &s;
>    ++ps->i;

Most C++ programmers would not.  Modern practice is to avoid naked
pointers when possible, which for me is almost all the time.  Pointers
are needed only for low -level programming, like building a new type
of container.  The rest of the time you can use auto_ptr or some other
smart pointer type.

Anyway, the arrow and dot operators have the same precedence, so I
don't see why you would prefer ++ps->i to ++s.i.  I find ++ps->i to be
more confusing, since a pointer can be incremented, so it would be
possible to read (++ps)->i.  A reference can not be incremented, so
there is only one reasonable interpretation of ++s.i.