On 03/16/2018 03:10 PM, H. S. Teoh wrote:
On Fri, Mar 16, 2018 at 02:58:36PM -0400, Steven Schveighoffer via
Digitalmars-d wrote:
On 3/16/18 2:07 PM, Seb wrote:
On Friday, 16 March 2018 at 17:50:37 UTC, Andrei Alexandrescu wrote:
On 3/16/18 1:41 PM, H. S. Teoh wrote:
Given a forward range r, I want to test whether it has exactly n
elements that satisfy some given predicate pred. Is it possible
to do this using current Phobos algorithms such that it does not
traverse more members of the range than necessary?
The naïve solution `r.count!pred == n` walks the entire range,
even though it may already have seen n+1 elements that satisfies
pred, and therefore should already know that the answer must be
false.
r.count!pred.walkLength(n) == n
Shouldn't this be using filter (count is eager)?
r.filter!pred.walkLength(n) == n
r.filter!pred.walkLength(n + 1) == n
[...]
Aha, so the trick is the 2-argument overload of walkLength. That's what
I was looking for. Thanks!
And yes, it should be .walkLength(n+1) because otherwise you don't know
if the actual count is >n.
Noice, thanks for the correx all.
