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//! Compile-time assertions to ensure that invariants are met. //! //! # Usage //! //! This crate is available [on crates.io][crate] and can be used by adding the //! following to your project's `Cargo.toml`: //! //! ```toml //! [dependencies] //! static_assertions = "0.1" //! ``` //! //! and this to your crate root: //! //! ``` //! #[macro_use] //! extern crate static_assertions; //! # fn main() {} //! ``` //! //! # Assert Equal Size //! //! When performing operations such as pointer casts or dealing with [`usize`] //! versus [`u64`] versus [`u32`], the size of your types matter. This is where //! [`assert_eq_size`] comes into play. Types provided as arguments to //! [`assert_eq_size`] are ensured to be the same size at compile-time. If the //! types differ in size, the code will fail to compile. //! //! ``` //! # #[macro_use] //! # extern crate static_assertions; //! # fn main() { //! assert_eq_size!([u8; 4], (u16, u16), u32); //! //! // Produces a compilation failure: //! // assert_eq_size!(u32, u8); //! # } //! ``` //! //! Similar to [`assert_eq_size`], there is [`assert_eq_size_val`]. Instead of //! specifying types to compare, values' sizes can be directly compared against //! each other. //! //! ``` //! # #[macro_use] //! # extern crate static_assertions; //! # fn main() { //! let x = 42u8; //! let y = true; //! //! assert_eq_size_val!(x, y); //! # } //! ``` //! [`assert_eq_size_val`] doesn't consume its arguments and thus works for //! non-[`Clone`]able values. //! //! ``` //! # #[macro_use] //! # extern crate static_assertions; //! # fn main() { //! struct Buffer([u8; 256]); //! //! let buf = Buffer([0; 256]); //! let val = [0u64; 32]; //! //! assert_eq_size_val!(buf, val); //! //! // `buf` and `val` can be used here //! # } //! ``` //! //! # Assert Constant Expression //! //! Constant expressions can be ensured to have certain properties via //! [`const_assert`]. If the expression evaluates to `false`, the file will fail //! to compile. This is synonymous to [`static_assert` in C++][static_assert]. //! //! ``` //! # #[macro_use] //! # extern crate static_assertions; //! # fn main() { //! const NUM: usize = 32; //! //! const_assert!(NUM * NUM == 1024); //! # } //! ``` //! //! As a shorthand for `const_assert!(a == b)`, there's [`const_assert_eq`]: //! //! ``` //! # #[macro_use] //! # extern crate static_assertions; //! # fn main() { //! const NUM: usize = 32; //! const_assert_eq!(NUM + NUM, 64); //! //! const TWO: usize = 2; //! const_assert_eq!(TWO * TWO, TWO + TWO, 4); //! # } //! ``` //! //! **Limitation:** Due to implementation details, [`assert_eq_size`], //! [`const_assert`], and [`const_assert_eq`] can only be used from within the //! context of a function. //! //! [crate]: https://crates.io/crates/static_assertions //! [static_assert]: http://en.cppreference.com/w/cpp/language/static_assert //! [`Clone`]: https://doc.rust-lang.org/std/clone/trait.Clone.html //! [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html //! [`u64`]: https://doc.rust-lang.org/std/primitive.u64.html //! [`u32`]: https://doc.rust-lang.org/std/primitive.u32.html //! [`assert_eq_size_val`]: macro.assert_eq_size_val.html //! [`assert_eq_size`]: macro.assert_eq_size.html //! [`const_assert`]: macro.const_assert.html //! [`const_assert_eq`]: macro.const_assert_eq.html #![no_std] #[doc(hidden)] pub extern crate core as _core; /// Asserts at compile-time that the types have equal sizes. /// /// This especially is useful for when coercing pointers between different types /// and ensuring the underlying values are the same size. /// /// # Example /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// struct Byte(u8); /// /// # fn main() { /// assert_eq_size!(Byte, u8); /// /// // Supports unlimited arguments: /// assert_eq_size!([Byte; 4], [u16; 2], u32); /// /// // Fails to compile: /// // assert_eq_size!(Byte, u16); /// # } /// ``` #[macro_export] macro_rules! assert_eq_size { ($x:ty, $($xs:ty),+) => { #[allow(unused_unsafe)] unsafe { use $crate::_core::mem::{forget, transmute, uninitialized}; $(forget::<$xs>(transmute(uninitialized::<$x>()));)+ } } } /// Asserts at compile-time that the values have equal sizes. /// /// # Example /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// # fn main() { /// struct Byte(u8); /// /// let x = 10u8; /// let y = Byte(42); // Works for non-cloneable types /// /// assert_eq_size_val!(x, y); /// assert_eq_size_val!(x, y, 0u8); /// /// // Fails to compile: /// // assert_eq_size_val!(x, 0u32); /// # } /// ``` #[macro_export] macro_rules! assert_eq_size_val { ($x:expr, $($xs:expr),+) => { #[allow(unused_unsafe)] unsafe { use $crate::_core::{mem, ptr}; let mut copy = ptr::read(&$x); $(ptr::write(&mut copy, mem::transmute(ptr::read(&$xs)));)+ mem::forget(copy); } } } /// Asserts at compile-time that the constant expression evaluates to `true`. /// /// # Example /// /// ``` /// # #[macro_use] /// # extern crate static_assertions; /// # fn main() { /// const_assert!(2 + 2 == 4); /// /// const FIVE: usize = 5; /// const_assert!(FIVE - FIVE == 0); /// /// // Fails to compile: /// // const_assert!(1 >= 2); /// # } /// ``` #[macro_export] macro_rules! const_assert { ($cond:expr) => { // Causes overflow if condition is false let _ = [(); 0 - (!($cond) as usize)]; }; ($($xs:expr),+) => { const_assert!($($xs)&&+); }; ($($xs:expr);+ $(;)*) => { const_assert!($($xs),+); }; } /// Asserts at compile-time that the constants are equal in value. #[macro_export] macro_rules! const_assert_eq { ($x:expr, $($xs:expr),+) => { const_assert!($($x == $xs),+); } }