You choose the algorithm that randomizes source values for a distribution by initializing it with an instance of any class that implements the GKRandom protocol, such as a basic random source (a subclass of GKRandomSource) or another random distribution. The GKRandomDistribution class itself implements a uniform distribution—for more specialized distributions use one of the subclasses GKGaussianDistribution and GKShuffledDistribution.
In a uniform distribution, the probability of generating any number in a specified range (between the values of the distribution’s lowestValue and highestValue properties) is approximately equal. In other words, there is no bias toward any possible outcome. To generate random numbers in this range, use the methods from the GKRandom protocol listed in Generating Random Numbers.