Updating to 0.7

Since the 0.6 release, rust-random gained a logo and a new crate: getrandom!


Rand crates now require rustc version 1.32.0 or later. This allowed us to remove all build.rs files for faster compilation.

The Rand crate now has fewer dependencies overall, though with some new ones.


As mentioned above, we have a new crate: getrandom, delivering a minimal API around platform-independent access to fresh entropy. This replaces the previous implementation in OsRng, which is now merely a wrapper.

Core features

The FromEntropy trait has now been removed. Fear not though, its from_entropy method continues to provide easy initialisation from its new home in the SeedableRng trait (this requires that rand_core has the std or getrandom feature enabled):

fn main() {
use rand::{SeedableRng, rngs::StdRng};
let mut rng = StdRng::from_entropy();

The SeedableRng::from_rng method is now considered value-stable: implementations should have portable results.

The Error type of rand_core and rand has seen a major redesign; direct usage of this type is likely to need adjustment.


These have seen less change than in the previous release, but noteworthy is:

  • rand_chacha has been rewritten for much better performance (via SIMD instructions)
  • StdRng and ThreadRng now use the ChaCha algorithm. This is a value-breaking change for StdRng.
  • SmallRng is now gated behind the small_rng feature flag.
  • The xoshiro crate is now rand_xoshiro.
  • rand_pcg now includes Pcg64.


For the most widely used distributions (Standard and Uniform), there have been no significant changes. But for most of the rest...

  • We added a new crate, rand_distr, to house the all distributions (including re-exporting those still within rand::distributions). If you previously used rand::distributions::Normal, now you use rand_distr::Normal.
  • Constructors for many distributions changed in order to return a Result instead of panicking on error.
  • Many distributions are now generic over their parameter type (in most cases supporting f32 and f64). This aids usage with generic code, and allows reduced size of parameterised distributions. Currently the more complex algorithms always use f64 internally.
  • Standard can now sample NonZeroU* values

We also added several distributions:


To aid portability, all random samples of type usize now instead sample a u32 value when the upper-bound is less than u32::MAX. This means that upgrading to 0.7 is a value-breaking change for use of seq functionality, but that after upgrading to 0.7 results should be consistent across CPU architectures.