🚀 go-pugleaf

In article <MATT.95Sep6110625@physics2.Berkeley.EDU>
martelli@cadlab.cadlab.it (Alex Martelli) writes:

|> kanze@gabi-soft.fr (J. Kanze) writes (in comp.lang.c++):
|> >Wil Evers (wil@ittpub.nl) wrote:
|> 	...
|> >|> 	array[index].doSomethingToIt(args);
|> 	...
|> >|> Please note that at least some compilers - I'm not sure if this is  
|> >|> standard-conforming - will accept the second syntax even when we're using  
|> >|> the proxy approach. They will call doSomethingToIt() on the temporary  
|> >|> returned by the array's get() member function and then discard it. In  
|> >|> other words, the array element at index is not changed at all!

|> in the context of something like (I'm synthesizing from word-level
|> descriptions by Kanze and Evers):

|> class A {
|>      ...
|> public:
|>      int doSomethingToIt(int args);
|> };

|> class proxyA;

|> class arrayA {
|>     ...
|> public;
|>     A& get(int index);
|>     void put(int index, const A&it);
|>     proxyA operator[](int index);
|> };

|> class proxyA {
|>      arrayA& thearray;
|>      int theindex;
|> public:
|>      proxyA(arrayA& inar, int inin): thearray(inar), theindex(inin) {}
|>      operator A() { return thearray.get(theindex); }
|>      void operator=(const A& it) { thearray.put(theindex, it); }
|> };


|> In this case, the behaviour Wil describes is not standard conforming,
|> I believe; conversions are NOT supposed to be applied to the implicit
|> "this" operator of any member function, here doSomethingToIt()!

Correct.

Depending on the case, you can either provide all necessary forwarding
functions (which can be painful if there are a lot, and is not even
possible for template classes) or overload operator->() in the proxy,
and make the user write ``a[ x ]->someFunction()'' instead of
``a[ x ].someFunction()''.  (What you really want to do is overload
operator.(), but the powers that be have decided otherwise.
--

James Kanze         Tel.: (+33) 88 14 49 00        email: kanze@gabi-soft.fr
GABI Software, Sarl., 8 rue des Francs-Bourgeois, F-67000 Strasbourg, France
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