Iterating over containers of immutable objects

[Justin Johansson]

To cut to the chase, what is the idiomatic code for iterating
over a container of immutable objects when the container provides
a "getIterator" method?

Alternatively, how can the following code be written
(1) to not use a break statement and,
(2) with casting away immutability.

Specifically my question is about assigning to an
immutable loop variable and not wanting to get
into any discussion about iterators and ranges per
se (unless relevant to the first bit).


// A class reprenting some abstract immutable item
immutable abstract class Bar
{
}

// A container of Bar immutable objects
abstract class BarContainer
{
   BarIterator getIterator();
}

// An interface for iterating over the
// immutable Bar objects in a BarContainer
interface BarIterator
{
   immutable(Bar) next();
}

void testBarIterator( BarContainer barContainer)
{
   auto iter = barContainer.getIterator();

   while (true) {
      auto bar = iter.next();

      if (bar is null)
         break;

      // process the bar item
      // ...
   }
}


So far so good, but having the break statement doesn't
seem all that clean.  My next try appeals better in style
to me but it doesn't compile, yielding

Error: variable test.testBarIterator2.bar cannot modify immutable

void testBarIterator2( BarContainer barContainer)
{
   auto iter = barContainer.getIterator();
   immutable Bar bar;

   while ((bar = iter.next()) !is null) {       // error line
      // process the bar item
      // ...
   }
}


Probably I've missed something but the answer alludes me.

Thanks
Justin Johansson