Function std.range.primitives.walkLength
This is a best-effort implementation of length for any kind of
range.
auto walkLength(Range)
(
Range range
)
if (isInputRange!Range && !isInfinite!Range);
auto walkLength(Range)
(
Range range,
const size_t upTo
)
if (isInputRange!Range);
If hasLength!Range, simply returns range without
checking upTo (when specified).
Otherwise, walks the range through its length and returns the number
of elements seen. Performes Ο(n) evaluations of range
and range, where n is the effective length of range.
The upTo parameter is useful to "cut the losses" in case
the interest is in seeing whether the range has at least some number
of elements. If the parameter upTo is specified, stops if upTo steps have been taken and returns upTo.
Infinite ranges are compatible, provided the parameter upTo is
specified, in which case the implementation simply returns upTo.
Example
import stdAuthors
Andrei Alexandrescu, David Simcha, and Jonathan M Davis. Credit for some of the ideas in building this module goes to Leonardo Maffi.