A Rust library for random number generation.
Rand provides utilities to generate random numbers, to convert them to useful types and distributions, and some randomness-related algorithms.
The core random number generation traits of Rand live in the rand_core crate but are also exposed here; RNG
implementations should prefer to use
rand_core while most other users should
Add this to your
[dependencies] rand = "0.6"
To get started using Rand, see The Book.
Rand libs have inter-dependencies and make use of the
semver trick in order to make traits
compatible across crate versions. (This is especially important for
SeedableRng.) A few crate releases are thus compatibility shims,
depending on the next lib version (e.g.
0.3.1). This means, for example, that
rand_core_0_3_0::SeedableRng are distinct, incompatible traits, which can
cause build errors. Usually, running
cargo update is enough to fix any issues.
The Rand lib is not yet stable, however we are careful to limit breaking changes and warn via deprecation wherever possible. Patch versions never introduce breaking changes. The following minor versions are supported:
- Version 0.6 was released in November 2018, redesigning the
seqmodule, moving most PRNGs to external crates, and many small changes.
- Version 0.5 was released in May 2018, as a major reorganisation
rand_core, and deprecating
Randand the previous distribution traits).
- Version 0.4 was released in December 2017, but contained almost no breaking changes from the 0.3 series.
A detailed changelog is available.
When upgrading to the next minor series (especially 0.4 → 0.5), we recommend reading the Upgrade Guide.
Rust version requirements
Since version 0.7 (unreleased), Rand requires Rustc version 1.32 or greater. Rand 0.5 requires Rustc 1.22 or greater while versions 0.4 and 0.3 (since approx. June 2017) require Rustc version 1.15 or greater. Subsets of the Rand code may work with older Rust versions, but this is not supported.
Travis CI always has a build with a pinned version of Rustc matching the oldest supported Rust release. The current policy is that this can be updated in any Rand release if required, but the change must be noted in the changelog.
To avoid bumping the required version unnecessarily, we use a
to auto-detect the compiler version and enable certain features or change code
paths automatically. Since this makes it easy to unintentionally make use of
features requiring a more recent Rust version, we recommend testing with a
pinned version of Rustc if you require compatibility with a specific version.
Rand is built with the
getrandom features enabled by default:
stdenables functionality dependent on the
stdlib and implies
getrandomis an optional crate, providing the code behind
rngs::OsRng; the continued existance of this feature is not guaranteed so users are encouraged to specify
The following optional features are available:
alloccan be used instead of
logenables some logging via the
nightlyenables all unstable features (
serde1enables serialization for some types, via Serde version 1.
simd_supportenables uniform sampling of SIMD types (integers and floats).
stdwebenables support for
wasm-bindgenenables support for
no_std mode is activated by setting
default-features = false; this removes
functionality depending on
random()are not available, as they require thread-local storage and an entropy source.
- Since no external entropy is available, it is not possible to create
generators with fresh seeds using the
FromEntropytrait (user must provide a seed).
- Several non-linear distributions distributions are unavailable since
logfunctions are not provided in
- Large parts of the
seq-uence module are unavailable, unless the
allocfeature is used (several APIs and many implementations require
Rand is distributed under the terms of both the MIT license and the Apache License (Version 2.0).