When are associative arrays meant to throw a RangeError?

[Ben Davis]

On 19/02/2012 15:05, Daniel Murphy wrote:
> "Ben Davis"<entheh at cantab.net>  wrote in message
> news:jhr0qf$24sj$1 at digitalmars.com...
>> On 19/02/2012 03:31, Daniel Murphy wrote:
>>> Except for this magic initialization, AAs behave the same as classes - ie
>>> a
>>> reference type.
>>
>> That's not quite true, because 'length' is passed around by value
>> alongside the reference, leading to semantics you could never reproduce
>> with classes, unless I'm mistaken.
>
> AAs, not Arrays.

Ah, well then I did this test earlier:

int[string] assoc=null;
writefln("%s",assoc.length);
//prints 0

Why did that work?