Providing implicit conversion of

[Gavin Gray via Digitalmars-d-learn]

The following code:

  ulong charlie = 11;
  long johnstone = std.algorithm.comparison.max(0, -charlie);
  writeln(format!"johnstone %s"(johnstone));
Results in (without any warning(s)):
johnstone -11

However you choose to look at it, this means -11 > 0 (regardless 
of all arguments concerning implicit conversions, 1's and 2's 
complements, being efficient, etc).

The language should not allow unary unsigned anything.