pub fn thread_rng() -> ThreadRng
Retrieve the lazily-initialized thread-local random number
generator, seeded by the system. Intended to be used in method
chaining style, e.g.
After generating a certain amount of randomness, the RNG will reseed itself from the operating system or, if the operating system RNG returns an error, a seed based on the current system time.
The internal RNG used is platform and architecture dependent, even
if the operating system random number generator is rigged to give
the same sequence always. If absolute consistency is required,
explicitly select an RNG, e.g.