Macro static_assertions::const_assert
source · macro_rules! const_assert { ($x:expr $(,)?) => { ... }; }
Expand description
Asserts that constant expressions evaluate to true
.
Constant expressions can be ensured to have certain properties via this
macro If the expression evaluates to false
, the file will fail to compile.
This is synonymous to static_assert
in C++.
§Alternatives
There also exists const_assert_eq
for
validating whether a sequence of expressions are equal to one another.
§Examples
A common use case is to guarantee properties about a constant value that’s generated via meta-programming.
const VALUE: i32 = // ...
const_assert!(VALUE >= 2);
Inputs are type-checked as booleans:
ⓘ
const_assert!(!0);
Despite this being a macro, we see this produces a type error:
| const_assert!(!0);
| ^^ expected bool, found integral variable
|
= note: expected type `bool`
found type `{integer}`
The following fails to compile because multiplying by 5 does not have an identity property:
ⓘ
const_assert!(5 * 5 == 5);