How to define an interator to provide array like behaviour in a class?

[Jonathan M Davis]

On Wednesday, October 17, 2012 00:03:46 Gary Willoughby wrote:
> I want to do something like this (Collection is a custom type):
> 
> Collection x = new Collection();
> x.add(something);
> x.add(somethingElse);
> 
> foreach(type value; x)
> {
> writeln(value);
> }
> 
> Collection is a class with a private array member variable which
> actually holds the collection data entered via the add method.
> What do i need to add to the Collection class to make it iterable
> (whilst it's actually iterating through the member array) so the
> foreach loop works as expected?

1. Define opApply (see section labeled "Foreach over Structs and Classes with 
opApply after here: http://dlang.org/statement.html#foreach_with_ranges)

2. Or make it a range (see http://dlang.org/statement.html#foreach_with_ranges 
and http://ddili.org/ders/d.en/ranges.html ), which would probably be a bad 
idea, since containers really shouldn't be ranges.

3. Or do what std.container does and overload opSlice which returns a range 
over the container (see http://dlang.org/operatoroverloading.html#Slice and 
http://dlang.org/phobos/std_container.html in addition to the links in #2). 
Overall, this is the best approach.

But regardless of which approach you take, you really should read up on ranges 
if you want to be doing much with D's standard library, and 
http://ddili.org/ders/d.en/ranges.html is the best tutorial on them at this 
point. There's also this recent article by Walter Bright which explains one of 
the main rationales behind ranges:

http://www.drdobbs.com/architecture-and-design/component-programming-in-
d/240008321

- Jonathan M Davis