Currently the Rand is bascially an implementation of ChaCha8, which is not ideal, as we want to provide multiple random number algorithms for different occasions. For example, we may want LCG as its fast and straightforward when we do not need cryptographic security.

A possible solution is to follow go's path, defining a Source trait, and define Rand as a wrapper around it:

pub(open) trait Source {
  next() -> UInt64
}

type Rand &Source

The migration, however, will break a couple of APIs, notably the new function.