Crate static_assertions

Compile-time assertions to ensure that invariants are met.

All assertions within this crate are performed at compile-time. This allows for finding errors quickly and early when it comes to ensuring certain features or aspects of a codebase. These macros are especially important when exposing a public API that requires types to be the same size or implement certain traits.

Usage

This crate is available on crates.io and can be used by adding the following to your project’s Cargo.toml:

[dependencies]
static_assertions = "0.3.0"

and this to your crate root (main.rs or lib.rs):

#[macro_use]
extern crate static_assertions;

Examples

Very thorough examples are provided in the docs for each individual macro. Failure case examples are also documented.

Limitations

Due to implementation details, some macros can only be used normally from within the context of a function. To use these macros in other contexts, a unique label must be provided.

// error: expected item after attributes
const_assert!(true == true);

This can be fixed via:

const_assert!(label; true == true);

This can be followed at issue #1.

Labeling Limitation Fix

The labeling workaround is not necessary (and is removed) when compiling on nightly Rust with the nightly feature flag enabled. This can be done by having the following in your project’s Cargo.toml:

[dependencies.static_assertions]
version  = "0.3.0"
features = ["nightly"]

To compile with nightly Rust, run the following in your shell or command prompt of choice:

rustup install nightly
cargo +nightly build

Notice that this also requires enabling the underscore_const_names nightly Rust feature:

#![feature(underscore_const_names)]

const_assert!(true != false);

fn main() {
    const_assert!(false != true);
}

Changes

See CHANGELOG.md for a complete list of what has changed from one version to another.

Donate

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Macros

assert_cfg

Asserts that a given configuration is set.

assert_eq_size

Asserts that types are equal in size.

assert_eq_size_ptr

Asserts that values pointed to are equal in size.

assert_eq_size_val

Asserts that values are equal in size.

assert_fields

Asserts that the type has the given fields.

assert_impl

Asserts that the type implements the given traits.

assert_obj_safe

Asserts that the traits are object-safe.

const_assert

Asserts that constant expressions evaluate to true.

const_assert_eq

Asserts that constants are equal in value.