https://issues.dlang.org/show_bug.cgi?id=19525

          Issue ID: 19525
           Summary: Duration is not usable with zero-arg std.algorithm.sum
           Product: D
           Version: D2
          Hardware: x86
                OS: Windows
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: simen.kjaras@gmail.com

Source: https://stackoverflow.com/questions/53967917/using-std-algorithm-iteration-sum-with-duration

import std.algorithm : sum;
import std.datetime : Duration, minutes;

unittest {
    // Error: struct `core.time.Duration` member this is not accessible
    assert([1.minutes].sum() == 1.minutes);
}

The above code fails because sum() tries to construct Duration(0), which fails
to compile. The error message (member this is not accessible) leaves something
to be desired.

Workaround for now: [1.minutes].sum(Duration.zero).

Suggested fix: have sum() check if Seed.zero exists, and use that.

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