RCR 270: Add clamp(), modulo(), rand() methods to Range

The Range object is <i>under-interpreted</i> as a range. As a Range object is not merely a duple of integers, there is room for more methods which take advantage of its meaning.

The Range class does not include all methods which are common operations on ranges.

Given than rng is a Range object:

• Add rng.clamp(n), which will return the value of n if n is within the range, or otherwise the minimum or maximum points in the range.
• Add rng.modulo(n), which will perform a modulus operation to assure that the return value is a member of rng.
• Similar to a comment in RCR 62, add rng.rand(), which will supply a random number from within the range.

Would cause no incompatibility problems; programmers would be free to use or not use these features.

# in addition to what is already there
class Range

  # returns a value within the range
  # will return lowest or highest
  # value if n is out of range in the
  # lower or upper directions
  # (respectively)
  def clamp(n)
    return first if n<first
    return last-1 if n>last-1 && exclude_end?
    return last if n>last
    n
  end

  # maps n to a value in the range.
  # this comes up in many algorithms.
  def modulo(n)
    n.modulo(length) + first
  end

  # choose a random member of this range
  def rand
    modulo Kernel::rand(length)
  end
end