[Issue 21695] New: Add three-way comparison function to std.functional

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=21695

          Issue ID: 21695
           Summary: Add three-way comparison function to std.functional
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P1
         Component: phobos
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

std.functional already contains the two-way comparison functions lessThan,
greaterThan, and equalTo. Since D supports three-way comparison natively via
opCmp, it should have a three-way comparison function too.

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