If you do this:
import std.algorithm : sum;
import core.time : Duration;
Duration[] parts;
auto total = parts.sum;
You'll get an error ("struct core.time.Duration member this is
not accessible"). That's because the Duration constructor is
private, and `sum` calls `sum(r, Unqual!Seed(0))`. BTW, not the
most helpful of messages for beginners, maybe this could be
phrased to say the ctor is private?
I suppose that the ctor is private due to the arbitrary nature of
its input units (hecto-nanoseconds), even though Duration(0) is
unambiguous. On the other hand, sum has to use Seed(0) instead of
Seed.init because some types don't use 0 as .init, namely floats.
The result is that you have to use range.sum(Duration.zero), or
Duration.init.
Something here rubs me the wrong way, but I can't tell exactly
what it is, or what can be done about it :)
