[swift-evolution] [Re-Review] SE-0104: Protocol-oriented integers

plx plxswift at icloud.com
Thu Feb 23 11:45:33 CST 2017

> On Feb 23, 2017, at 11:31 AM, David Sweeris <davesweeris at mac.com> wrote:
> On Feb 23, 2017, at 07:33, plx via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Next quibble: `Magnitude` being defined as the “absolute value” of the underlying type seems a bit nonsensical if e.g. `Number` is intended to be adoptable by complex numbers (let alone quaternions, matrices, and whatnot). What *would* a conforming complex # implementation be expected to return as e.g. `(1-i).magnitude`?
> sqrt(2), I believe, or as close to it as can be represented by `Magnitude`

…which is what I’d expect if `x.magnitude` is supposed to be `||x||` or whatnot, but the stated motivation is:

  /// The magnitude of this value.
  /// For any numeric value `x`, `x.magnitude` is the absolute value of `x`.
  /// You can use the `magnitude` property in operations that are simpler to
  /// implement in terms of unsigned values, such as printing the value of an
  /// integer, which is just printing a '-' character in front of an absolute
  /// value.
  ///     let x = -200
  ///     // x.magnitude == 200

…for which uses the norm is not really helpful (and `Magnitude` not being `Comparable` is pretty annoying if it’s intended to be a norm; it really seems only intended to work as a generic tool for writing pretty-printers).

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