[](https://github.com/nvzqz/static-assertions-rs)
<div align="center">
<a href="https://crates.io/crates/static_assertions">
<img src="https://img.shields.io/crates/v/static_assertions.svg" alt="Crates.io">
<img src="https://img.shields.io/crates/d/static_assertions.svg" alt="Downloads">
</a>
<a href="https://travis-ci.org/nvzqz/static-assertions-rs">
<img src="https://travis-ci.org/nvzqz/static-assertions-rs.svg?branch=master" alt="Build Status">
</a>
<img src="https://img.shields.io/badge/rustc-^1.37.0-blue.svg" alt="rustc ^1.37.0">
<br>
<a href="https://www.patreon.com/nvzqz">
<img src="https://c5.patreon.com/external/logo/become_a_patron_button.png" alt="Become a Patron!" height="35">
</a>
<a href="https://www.paypal.me/nvzqz">
<img src="https://buymecoffee.intm.org/img/button-paypal-white.png" alt="Buy me a coffee" height="35">
</a>
</div>
Compile-time assertions for Rust, brought to you by
[Nikolai Vazquez](https://twitter.com/NikolaiVazquez).
This library lets you ensure correct assumptions about constants, types, and
more. See the [docs] and [FAQ](#faq) for more info!
## Installation
This crate is available
[on crates.io](https://crates.io/crates/static_assertions) and can be used by
adding the following to your project's
[`Cargo.toml`](https://doc.rust-lang.org/cargo/reference/manifest.html):
```toml
[dependencies]
static_assertions = "1.1.0"
```
and this to your crate root (`main.rs` or `lib.rs`):
```rust
#[macro_use]
extern crate static_assertions;
```
## Usage
This crate exposes the following macros:
- [`assert_cfg!`]
- [`assert_eq_align!`]
- [`assert_eq_size!`]
- [`assert_eq_size_ptr!`]
- [`assert_eq_size_val!`]
- [`assert_fields!`]
- [`assert_impl_all!`]
- [`assert_impl_any!`]
- [`assert_impl_one!`]
- [`assert_not_impl_all!`]
- [`assert_not_impl_any!`]
- [`assert_obj_safe!`]
- [`assert_trait_sub_all!`]
- [`assert_trait_super_all!`]
- [`assert_type_eq_all!`]
- [`assert_type_ne_all!`]
- [`const_assert!`]
- [`const_assert_eq!`]
- [`const_assert_ne!`]
## FAQ
- **Q:** When would I want to use this?
**A:** This library is useful for when wanting to ensure properties of
constants, types, and traits.
Basic examples:
- With the release of 1.39, `str::len` can be called in a `const`
context. Using [`const_assert!`], one can check that a string generated from
elsewhere is of a given size:
```rust
const DATA: &str = include_str!("path/to/string.txt");
const_assert!(DATA.len() < 512);
```
- Have a type that absolutely must implement certain traits? With
[`assert_impl_all!`], one can ensure this:
```rust
struct Foo {
value: }
assert_impl_all!(Foo: Send, Sync);
```
- **Q:** How can I contribute?
**A:** A couple of ways! You can:
- Attempt coming up with some form of static analysis that you'd like to see
implemented. Create a [new issue] and describe how you'd imagine your
assertion to work, with example code to demonstrate.
- Implement your own static assertion and create a [pull request].
- Give feedback. What are some pain points? Where is it unpleasant?
- Write docs. If you're familiar with how this library works, sharing your
knowledge with the rest its users would be great!
- **Q:** Will this affect my compiled binary?
**A:** Nope! There is zero runtime cost to using this because all checks are
at compile-time, and so no code is emitted to run.
- **Q:** Will this affect my compile times?
**A:** Likely not by anything perceivable. If this is a concern, this library
can be put in `dev-dependencies`:
```toml
[dev-dependencies]
static_assertions = "1.1.0"
```
and then assertions can be conditionally run behind `#[cfg(test)]`:
```rust
#[cfg(test)]
const_assert_eq!(MEANING_OF_LIFE, 42);
```
However, the assertions will only be checked when running `cargo test`. This
somewhat defeats the purpose of catching false static conditions up-front with
a compilation failure.
- **Q:** What is `const _`?
**A:** It's a way of creating an unnamed constant. This is used so that macros
can be called from a global scope without requiring a scope-unique label. This
library makes use of the side effects of evaluating the `const` expression.
See the feature's
[tracking issue](https://github.com/rust-lang/rust/issues/54912)
and
[issue #1](https://github.com/nvzqz/static-assertions-rs/issues/1)
for more info.
## Changes
See [`CHANGELOG.md`](https://github.com/nvzqz/static-assertions-rs/blob/master/CHANGELOG.md)
for a complete list of what has changed from one version to another.
## License
This project is released under either:
- [MIT License](https://github.com/nvzqz/static-assertions-rs/blob/master/LICENSE-MIT)
- [Apache License (Version 2.0)](https://github.com/nvzqz/static-assertions-rs/blob/master/LICENSE-APACHE)
at your choosing.
[new issue]: https://github.com/nvzqz/static-assertions-rs/issues/new
[pull request]: https://github.com/nvzqz/static-assertions-rs/pulls
[docs]: https://docs.rs/static_assertions
[`assert_cfg!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_cfg.html
[`assert_eq_align!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_eq_align.html
[`assert_eq_size!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_eq_size.html
[`assert_eq_size_ptr!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_eq_size_ptr.html
[`assert_eq_size_val!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_eq_size_val.html
[`assert_fields!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_fields.html
[`assert_impl_all!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_impl_all.html
[`assert_impl_any!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_impl_any.html
[`assert_impl_one!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_impl_one.html
[`assert_not_impl_all!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_not_impl_all.html
[`assert_not_impl_any!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_not_impl_any.html
[`assert_obj_safe!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_obj_safe.html
[`assert_trait_sub_all!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_trait_sub_all.html
[`assert_trait_super_all!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_trait_super_all.html
[`assert_type_eq_all!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_type_eq_all.html
[`assert_type_ne_all!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.assert_type_ne_all.html
[`const_assert!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.const_assert.html
[`const_assert_eq!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.const_assert_eq.html
[`const_assert_ne!`]: https://docs.rs/static_assertions/1.1.0/static_assertions/macro.const_assert_ne.html