https://issues.dlang.org/show_bug.cgi?id=21191

          Issue ID: 21191
           Summary: min should be stable: when in doubt, return the first
                    argument
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: normal
          Priority: P1
         Component: phobos
          Assignee: nobody@puremagic.com
          Reporter: andrei@erdani.com

This should work:

@safe unittest
{
    import std.algorithm;
    assert(min(1.0, double.nan) == 1.0);
    assert(min(double.nan, 1.0) is double.nan);
    static struct A {
        int x;
        string y;
        int opCmp(A a) { return int(x > a.x) - int(x < a.x); }
    }
    assert(min(A(1, "first"), A(1, "second")) == A(1, "first"));
}

In other words, min should return its first argument unless it makes a positive determination that the second argument "deserves" to be returned instead.

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