Cost of assoc array?

[Chris via Digitalmars-d-learn]

On Wednesday, 14 May 2014 at 11:13:10 UTC, John Colvin wrote:
> On Wednesday, 14 May 2014 at 09:38:10 UTC, Chris wrote:
>> I have code that uses the following:
>>
>> string[][size_t] myArray;
>>
>> 1. myArray = [0:["t", "o", "m"], 1:["s", "m", "i", "th"]];
>>
>> However, I've found out that I never need an assoc array and a 
>> "linear" array would be just fine, as in
>>
>> 2. myArray = [["t", "o", "m"], ["s", "m", "i", "th"]];
>>
>> Is there any huge difference as regards performance and memory 
>> footprint between the two? Or is 2. basically 1. under the 
>> hood?
>
> If you don't need the features of associative arrays, don't use 
> them.
>
> Normal arrays are much simpler, faster and (due to some 
> outstanding problems with associative arrays in D) less 
> bug-prone. Associative arrays, by definition, require a lot 
> more work behind the scenes for both reading and writing.

The question is, if they are _much_ faster. With this type 
(string[][size_t]) I haven't encountered any bugs yet. On the 
other hand, it introduces some rather stilted logic sometimes, as 
in

foreach (size_t i; 0..myArray.length) {
   // do something with myArray[i];
}

because it's not sorted. This, or I sort it first. Anyway, 
there's always an overhead associated with associative arrays. 
I'll have to see how big this breaking change would be, and 
decide, if it's worth it.

Profiling is not really feasible, because for this to work 
properly, I would have to introduce the change first to be able 
to compare both. Nothing worse than carefully changing things 
only to find out, it doesn't really speed up things.