On Thursday, 20 February 2014 at 09:42:34 UTC, Gopan wrote:
const uint n = among(3, 1,2,5,3); //no error
int[n] arr; //no error.
And,
int v = 3;
const uint n = among(v, 1,2,5,3); //Error: variable v cannot be
read at compile time
int[n] arr; Error: Integer constant expression expected instead
of among(v, 1, 2, 5, 3)
My conclusion is that when both 'v' and 'vals' are known at
compile time, the complexity is perfectly O(1). I would even
like to say O(0) at runtime :)
And, when either 'v' or 'vals' is not known at compile time,
the complexity is O(vals.length) because the computation
happens at runtime.
When v and vals are known at compile time, that opens up the
possibility of CTFE. It's necessary but not sufficient. When a
value is needed at compile time (e.g. initializer for a static
variable, length of a static array), then CTFE is forced. When
the value is not needed at compile time, the optimizer may go for
it, but that's not guaranteed.
