array idioms

[Steven Schveighoffer]

On Fri, 25 Feb 2011 15:09:44 -0500, Jonathan M Davis <jmdavisProg at gmx.com>  
wrote:

> On Friday, February 25, 2011 11:30:28 spir wrote:
>> Hello,
>>
>> What's the idiomatic way to:
>>
>> * delete an element in an associative array
>
> If you have the key, then just use remove. The online documentation for
> asseciative array discusses it. e.g.
>
> b.remove("hello");
>
> If you're looking to remove by value, however, you're going to have to  
> figure out
> what its key is. And if you want to remove _all_ elements with the same  
> value,
> then you're going to need to find _all_ of their keys. The best way to  
> do that
> would probably just be to use a foreach loop:
>
> foreach(k, v; aa)
> {
>     if(v == value)
>         aa.remove(k);
> }
>
> I'm not sure if there are any problems with removing from an associative  
> array
> while iterating over it though. I wouldn't think so, but I don't know  
> so. Worst
> case though, you save the list of keys to remove and then remove them  
> all once
> you have them all.

It is illegal to remove from an AA you are iterating.  I've learned first  
hand that this causes subtle memory bugs.  Do not do this.

However, dcollections supports this idiom via the purge operation:

foreach(ref doPurge, v; &mymap.purge)
    doPurge = (v == value);

-Steve