# rand_core
[](https://github.com/rust-random/rand/actions)
[](https://crates.io/crates/rand_core)
[](https://rust-random.github.io/book/)
[](https://rust-random.github.io/rand/rand_core)
[](https://docs.rs/rand_core)
[](https://github.com/rust-random/rand#rust-version-requirements)
Core traits and error types of the [rand] library, plus tools for implementing
RNGs.
This crate is intended for use when implementing the core trait, `RngCore`; it
defines the core traits to be implemented as well as several small functions to
aid in their implementation and types required for error handling.
The main [rand] crate re-exports most items defined in this crate, along with
tools to convert the integer samples generated by `RngCore` to many different
applications (including sampling from restricted ranges, conversion to floating
point, list permutations and secure initialisation of RNGs). Most users should
prefer to use the main [rand] crate.
Links:
- [API documentation (master)](
https://rust-random.github.io/rand/rand_core)
- [API documentation (docs.rs)](
https://docs.rs/rand_core)
- [Changelog](
https://github.com/rust-random/rand/blob/master/rand_core/CHANGELOG.md)
[rand]:
https://crates.io/crates/rand
## Functionality
The `rand_core` crate provides:
- base random number generator traits
- error-reporting types
- functionality to aid implementation of RNGs
The traits and error types are also available via `rand`.
## Versions
The current version is:
```
rand_core = "0.6.0"
```
Rand libs have inter-dependencies and make use of the
[semver trick](
https://github.com/dtolnay/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.
## Crate Features
`rand_core` supports `no_std` and `alloc`-only configurations, as well as full
`std` functionality. The differences between `no_std` and full `std` are small,
comprising `RngCore` support for `Box<R>` types where `R: RngCore`,
`std::io::Read` support for types supporting `RngCore`, and
extensions to the `Error` type's functionality.
The `std` feature is *not enabled by default*. This is primarily to avoid build
problems where one crate implicitly requires `rand_core` with `std` support and
another crate requires `rand` *without* `std` support. However, the `rand` crate
continues to enable `std` support by default, both for itself and `rand_core`.
The `serde1` feature can be used to derive `Serialize` and `Deserialize` for RNG
implementations that use the `BlockRng` or `BlockRng64` wrappers.
# License
`rand_core` is distributed under the terms of both the MIT license and the
Apache License (Version 2.0).
See [LICENSE-APACHE](LICENSE-APACHE) and [LICENSE-MIT](LICENSE-MIT), and
[COPYRIGHT](COPYRIGHT) for details.
