Re: Variables in for loop (style issue)

From:
brangdon@cix.co.uk (Dave Harris)
Newsgroups:
comp.lang.c++.moderated
Date:
23 May 2006 10:07:20 -0400
Message-ID:
<memo.20060522153352.3536A@brangdon.cix.compulink.co.uk>
thorsten.ottosen@dezide.com (Thorsten Ottosen) wrote (abridged):

It's not feasible, for example, to have an immutable container,
say, like std::vector<T>.


Actually it is. For example, Java's string class is immutable. Some
of us
wish C++ had an immutable string class too.

[return by const reference example snipped]
In Java, C# and D you can't do it without breaking encapsulation or
without copying the entire collection before returning a handle.


To do the equivalent in Java you would need to write the const
version of
the interface by hand. For example:

     struct ConstPoint {
         int x();
         int y();
         // ...
     };

     struct Point: ConstPoint {
         int set_x();
         int set_y();
         void operator=( ConstPoint &rhs );
         // ...
     };

     struct Rect {
         ConstPoint &top_left() { return top_left_; }
         void set_top_left( ConstPoint &tl ) { top_left = tl; }
         //...
     private:
         Point top_left_;
     };

 From a clients point of view, there's not much difference between
"const
Point" and "ConstPoint".

"Const" is a type operator. It creates a new type from an old one by
stripping out the non-const member functions. You can write the same
interface by hand.

-- Dave Harris, Nottingham, UK.

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