Random

Random.new(seed) makes a generator of random numbers from a seed. The same seed gives the same numbers every run, on every platform and after every upgrade, so a model made with random numbers is the same model each time it is built. There is no unseeded Random: to vary a model, make the seed a parameter.

The generator is SplitMix64, written in KupCAD rather than taken from a library, so a seed’s numbers don’t change with the platform or a dependency.

seed = param(:seed, default: 42)
g = Random.new(seed)
studs = (0...8).map do
  x = g.rand(0..90)
  y = g.rand(0..40)
  cylinder(r: 2, h: 3).translate(x, y, 2)
end
cube(x: 100, y: 50, z: 2).union(studs)

Random.new

Random.new(seed)

A generator seeded with seed, a whole number of magnitude up to 2^53.

Returns: Random.

Raises: ArgumentError without a seed, or for one that isn’t such a whole number.

rand

g.rand
g.rand(limit)
g.rand(range)

The next number from the generator:

Call	Gives
rand	A float in [0, 1).
rand(n)	A whole number from 0 to n - 1 for a whole n, else a float in [0, n).
rand(a..b)	A whole number from a to b for whole ends (a...b leaves b out), else a float from a up to b.

Returns: Number.

Raises: ArgumentError for a limit of 0 or less, an empty Range or one with a step; TypeError for anything but a Number or a Range.

shuffle

g.shuffle(array)

A copy of array in an order drawn from the generator; array itself is left as it was.

Returns: Array.

sample

g.sample(array)

One item of array, each equally likely.

Returns: the item, or nil for an empty Array.

seed

g.seed

The seed the generator was made with. Returns: Number.

g = Random.new(7)
a = g.rand(1..6)
h = Random.new(7)
puts h.rand(1..6) == a                    # true: the same seed, the same numbers
puts g.shuffle([1, 2, 3]).sort.inspect    # [1, 2, 3]
puts g.seed                               # 7
puts g.inspect                            # #<Random seed: 7>