Why function template 'among' is of complexity O(1) and not O(n)?

[Dicebot]

On Wednesday, 19 February 2014 at 13:03:38 UTC, Tobias Pankrath 
wrote:
> On Wednesday, 19 February 2014 at 09:46:04 UTC, Gopan wrote:
>> Index of 3 in (1,2,5,3) is 4
>>
>> Or, is my undertanding about Big-O notation of complexity 
>> wrong?
>>
>> Thanks,
>> Gopan
>
> O(1) = O(k) for any constant k.

I don't think it is legit to speak about k as constant here. It 
is constant for any specific function instance but not for 
template meta-algorithm as a whole.