Revamping associative arrays

[Christopher Wright]

Moritz Warning wrote:
> On Sat, 17 Oct 2009 18:58:08 +0000, BCS wrote:
>> what will this do?
>>
>> foreach(key; aa.keys)
>>    if(Test(key))
>>       aa.remove(key);
> 
> It's undefined behavior.
> You shouldn't try to mutate the aa while iterating.
> I hope that will be fixed.
> It took me some time to find this out.

That's really annoying, and it's true of most (all?) C# base class 
library collections. When coding in C#, I often find myself doing:

var remove = new HashedSet<Foo>();
foreach (var foo in foos)
	if (Test(foo)) remove.Add(foo);
foos.RemoveAll(remove);

It's more allocation than necessary, but more than that, it's an 
unnecessarily complicated way of interacting with the collection.