negate is a simple attribute macro that negates a given function.
Given a function of the form is_*
that returns a boolean value, the macro will create a is_not_*
function that negates the given function.
struct Word(&'static str);
impl Word {
pub fn new(word: &'static str) -> Self {
Self (word)
}
#[negate] // <- negate will implement a `is_not_uppercase` function!
pub fn is_uppercase(&self) -> bool {
self.0 == self.0.to_uppercase()
}
}
let my_name = Word::new("My Name");
assert!(my_name.is_not_uppercase());
Using the name attribute allows you to set the name of the generated function. This also allows the usage of the [negate] macro with functions that do not start with is_
.
use negate::negate;
pub enum TaskState {
Ready,
Finished,
}
pub struct Reactor {
tasks: HashMap<usize, TaskState>,
}
impl Reactor {
// Generates the `is_finished` function
#[negate(name = "is_finished")]
pub fn is_ready(&self, id: usize) -> bool {
self.tasks.get(&id).map(|state| match state {
TaskState::Ready => true,
_ => false,
}).unwrap_or(false)
}
}
Using the docs attribute allows you to customize the doc-string of the generated function.
use negate::negate;
#[negate(name = "is_odd", docs = "returns true if the given number is odd")]
fn is_even(x: i32) -> bool {
x % 2 == 0
}
assert!(is_odd(5));
#[negate]
pub fn is_even(x: i32) -> bool {
x % 2 == 0
}
Will expand to:
pub fn is_even(x: i32) -> bool {
x % 2 == 0
}
/// This is an automatically generated function that denies [`is_even`].
/// Consult the original function for more information.
pub fn is_not_even(x: i32) -> bool {
!is_even(x)
}
Using generics is likewise not a problem
#[negate]
fn is_equal<T>(x: T, y: T) -> bool
where
T: Eq,
{
x == y
}
The generated negated function:
/// This is an automatically generated function that denies [`is_equal`].
/// Consult the original function for more information.
fn is_not_equal<T>(x: T, y: T) -> bool
where
T: Eq,
{
!is_equal(x, y)
}
struct BigInt {
..
};
impl BigInt {
#[negate(name = "is_negative", docs = "Returns true if the number is negative and false if the number is zero or positive.")]
pub fn is_positive(&self) -> bool { .. }
}
Becomes:
impl BigInt {
pub fn is_positive(&self) -> bool { .. }
/// Returns true if the number is negative and false if the number is zero or positive.
pub fn is_negative(&self) -> bool {
!self.is_positive()
}
}