associative arrays: iteration is finally here

[Pelle Månsson]

Lars T. Kyllingstad wrote:
> Pelle Månsson wrote:
>> Lars T. Kyllingstad wrote:
>>> Pelle Månsson wrote:
>>>> Andrei Alexandrescu wrote:
>>>>> Pelle Månsson wrote:
>>>>>> Also, foreach with a single variable should default to keys, in my 
>>>>>> opinion.
>>>>>
>>>>> That is debatable as it would make the same code do different 
>>>>> things for e.g. vectors and sparse vectors.
>>>>>
>>>>>
>>>>> Andrei
>>>>
>>>> Debatable indeed, but I find myself using either just the keys or 
>>>> the keys and values together, rarely just the values. Maybe that's 
>>>> just me.
>>>
>>>
>>> I've used iteration over values more often than iteration over keys.
>>>
>>> Besides, I think consistency is important. Since the default for an 
>>> ordinary array is to iterate over the values, it should be the same 
>>> for associative arrays.
>>>
>>> -Lars
>> I don't understand this, when do you want the values without the keys? 
>> If you do, shouldn't you be using a regular array?
> 
> Here's an example:
> 
>    class SomeObject { ... }
>    void doStuffWith(SomeObject s) { ... }
>    void doOtherStuffWith(SomeObject s) { ... }
> 
>    // Make a collection of objects indexed by ID strings.
>    SomeObject[string] myObjects;
>    ...
> 
>    // First I just want to do something with one of the
>    // objects, namely the one called "foo".
>    doStuffWith(myObjects["foo"]);
> 
>    // Then, I want to do something with all the objects.
>    foreach (obj; myObjects)  doOtherStuffWith(obj);
> 
> Of course, if iteration was over keys instead of values, I'd just write
> 
>    foreach (id, obj; myObjects)  doOtherStuffWith(obj);
> 
> But then again, right now, when iteration is over values and I want the 
> keys I can just write the same thing. It all comes down to preference, 
> and I prefer things the way they are now. :)
> 
> 
>> Actually, it doesn't matter all that much, as long as we get .keys and 
>> .values as alternatives.
> 
> I still think the default for foreach should be consistent with normal 
> arrays.
> 
> -Lars
I think foreach should be consistent with opIn, that is,
if (foo in aa) { //it is in the aa.
   foreach (f; aa) { // loop over each item in the aa
     //I expect foo to show up in here, since it is "in" the aa.
   }
}

I use key iteration more than I use value iteration, and it is what I am 
used to. It is, as you say, a matter of preference.