class XSemVer::PreRelease

def <=>(other)
  
  # A SemVer with no prerelease data is 'greater' than a SemVer with any prerelease data.
  # If both prereleases are empty, they are equal.
  return  1 if  empty? && !other.empty?
  return -1 if !empty? &&  other.empty?
  return  0 if  empty? &&  other.empty?
  
  [ids.size, other.ids.size].max.times do |n|
    id = ids[n]
    oid = other.ids[n]
    
    # A pre-release with fewer ids is less than a pre-release with more ids. (1.0.0-alpha < 1.0.0-alpha.1)
    return 1 if oid.nil?
    return -1 if id.nil?
    
    # If a pre-release id consists of only numbers, it is compared numerically.
    if id =~ ONLY_DIGITS && oid =~ ONLY_DIGITS
      id = id.to_i
      oid = oid.to_i
    end
    
    # If a pre-release id contains one or more letters, it is compared alphabetically.
    comparison = (id <=> oid)
    return comparison unless comparison == 0
  end
  
  0
end