rand 0.7.3

Random number generators and other randomness functionality.


Build Status Build Status Crate Book API API Minimum rustc version

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 depend on rand.



Add this to your Cargo.toml:

rand = "0.7"

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 RngCore and SeedableRng.) A few crate releases are thus compatibility shims, depending on the next lib version (e.g. rand_core versions 0.2.2 and 0.3.1). This means, for example, that rand_core_0_4_0::SeedableRng and 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 0.7 was released in June 2019, moving most non-uniform distributions to an external crate, moving from_entropy to SeedableRng, and many small changes and fixes.
  • Version 0.6 was released in November 2018, redesigning the seq module, moving most PRNGs to external crates, and many small changes.
  • Version 0.5 was released in May 2018, as a major reorganisation (introducing RngCore and rand_core, and deprecating Rand and 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.

Yanked versions

Some versions of Rand crates have been yanked ("unreleased"). Where this occurs, the crate's CHANGELOG should be updated with a rationale, and a search on the issue tracker with the keyword yank should uncover the motivation.

Rust version requirements

Since version 0.7, 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.

Crate Features

Rand is built with these features enabled by default:

  • std enables functionality dependent on the std lib
  • alloc (implied by std) enables functionality requiring an allocator (when using this feature in no_std, Rand requires Rustc version 1.36 or greater)
  • getrandom (implied by std) is an optional dependency providing the code behind rngs::OsRng

Optionally, the following dependencies can be enabled:

  • log enables logging via the log crate
  • stdweb implies getrandom/stdweb to enable getrandom support on wasm32-unknown-unknown (will be removed in rand 0.8; activate via getrandom crate instead)
  • wasm-bindgen implies getrandom/wasm-bindgen to enable getrandom support on wasm32-unknown-unknown (will be removed in rand 0.8; activate via getrandom crate instead)

Additionally, these features configure Rand:

  • small_rng enables inclusion of the SmallRng PRNG
  • nightly enables all experimental features
  • simd_support (experimental) enables sampling of SIMD values (uniformly random SIMD integers and floats)

Rand supports limited functionality in no_std mode (enabled via default-features = false). In this case, OsRng and from_entropy are unavailable (unless getrandom is enabled), large parts of seq are unavailable (unless alloc is enabled), and thread_rng and random are unavailable.


Rand is distributed under the terms of both the MIT license and the Apache License (Version 2.0).