In Expression for Static and DYnamic Arrays

[Jonathan M Davis]

On Thursday, October 11, 2012 18:45:36 Rizo Isrof wrote:
> Hi,
> 
> Why the `in` expression can only be applied to associative
> arrays and cannot be used with static or dynamic arrays as
> it is possible with, _e.g._, Python?
> 
> The following code is not legal:
> ----
> int[] a = [1,2,3,4,5];
> if (1 in a) { }
> ----
> Are there any technical explanation for this limitation?

Because that would mean than in was O(n), whereas it's generally assumed to be 
at least o(log n) (which is what you'd get in a balanced binary tree such as 
red-black tree). AA's do it in O(1), so they're okay, but dynamic arrays can't 
do better than O(n). And if you can't rely on a certain algorithmic complexity 
for an operation, then it becomes problematic for generic code. std.container 
specifically lists the complexity requirements for every function in there 
which is standard across containers, and any container which can't define such 
a function in the required complexity, doesn't define that function.

There has been some discussion of allowing in on dynamic or static arrays in 
some restricted cases where the array is known at compile time, but nothing 
has come of it as of yet. Regardless, there's pretty much no way that arrays 
in general will ever work with in, because it would be too inefficent.

You can use std.algorithm.find or std.algorithm.canFind. e.g.

int[] a = [1, 2, 3, 4, 5];

if(canFind(a, 1))
{
 ...
}

- Jonathan M Davis