On Fri, Mar 27, 2009 at 00:22, Paul Ishenin <webpi...@mail.ru> wrote: > > FOR s IN list DO > WriteLn(s); > > extended: > > FOR s IN list USING my_reverse_iterator DO > WriteLn(s); > > In upper case I wrote keywords and in lower case identifiers.
I think the extension can be avoided like so: FOR s IN reverse(list) DO where reverse is a standard (or user-defined) function returning iterator. FOR s IN list DO will be a syntax sugar for FOR s IN default_iterator(list) DO where default_iterator is defined for built-in containers and can be redefined for user-defined ones. This can _almost_ be emulated at the library level -- look at the attached example. However, few problems exist: 1) overloading of operator := was designed without thinking, it should be a procedure with 'var' parameter instead of a function, because assignment often requires access to a previous state of l-value. So, rather ugly 'property V' is required. 2) 'while ForEach(a, r) do' is IMO less clear syntax than 'for a in r do' 3) user have to declare 'a: TIntegerArrayIterator' instead of simply 'a: Integer' 4) Note that I overloaded operator + only. In practice, all relevant operators should be overloaded, which is bulky. 5) Finally, all this code have to be written for every container/element combination. Generics might or might not help here -- but at this stage built-in implementation would actually be simpler then library-based one. -- Alexander S. Klenin
iter.pp
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