About the in expression, Why can't use with array.

[Dennis]

On Friday, 25 October 2019 at 05:17:35 UTC, Ali Çehreli wrote:
> - Big O is different

No it isn't. Worst case lookup of an associative array lookup is 
O(n) too. It can easily be 'achieved' by having a key type with:
```
size_t toHash() const scope pure {
     return 0;
}
```

The fact that std.container specifies a worst-case time 
complexity for operations on its data structures doesn't mean 
every other type has to comply to those too.
I can overload the 'in' operator on my types to something that 
takes exponential time if I want, just like "+" can also be 
overloaded to a linear time operation on e.g. BigInt.

> - One wants to use keys for associative arrays but (likely) 
> values for arrays

Then we implement `in` to look for values in arrays, just like 
users would expect.