attr-bounds 0.1.0

An attribute macro to apply bounds to items.
Documentation 
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use attr_bounds::bounds;

#[test]
fn empty_bounds() {
    #[bounds()]
    struct Wrapper<T>(T);

    let _ = Wrapper(42);
}

#[test]
fn enum_bounds() {
    #[bounds(A: std::fmt::Display)]
    #[bounds(B: std::ops::Add<Output = B>)]
    #[derive(Debug)]
    enum Either<A, B> {
        Left(A),
        Right(B),
    }

    let left = Either::<&str, i32>::Left("foo");
    let right = Either::<&str, i32>::Right(42);
    assert_eq!(format!("{left:?}"), "Left(\"foo\")");
    assert_eq!(format!("{right:?}"), "Right(42)");
}

#[test]
fn fn_bounds() {
    #[bounds(T: Clone)]
    fn clone<T>(var: &T) -> T {
        var.clone()
    }

    let v1 = vec![1, 2, 3];
    let v2 = clone(&v1);
    assert_eq!(v1, v2);
}

#[test]
fn assoc_fn_bounds() {
    trait Display {
        #[bounds(T: std::fmt::Display)]
        fn display<T>(var: T);
    }

    impl Display for () {
        #[bounds(T: std::fmt::Display)]
        fn display<T>(var: T) {
            println!("{var}");
        }
    }

    <()>::display(42);
}

#[test]
fn impl_bounds() {
    use std::{fmt::Display, ops::Add};

    trait Foo<T>
    where
        T: Copy + Display + Add<Output = T>,
    {
        fn foo(self, x: T) -> String;
    }

    #[bounds(S: Display)]
    #[bounds(T: Copy + Display + Add<Output = T>)]
    impl<S, T> Foo<T> for S {
        fn foo(self, x: T) -> String {
            self.to_string() + &(x + x).to_string()
        }
    }

    assert_eq!(42i32.foo(42i64), "4284");
}

#[test]
fn struct_bounds() {
    #[bounds(T: std::ops::Add<Output = T>)]
    #[derive(Debug)]
    struct Wrapper<T>(T);

    let var = Wrapper(42);
    assert_eq!(format!("{var:?}"), "Wrapper(42)");
}

#[test]
fn trait_bounds() {
    #[bounds(Self: Clone + std::ops::Mul<Output = Self>)]
    trait Square {
        fn square(&self) -> Self;
    }

    impl Square for i32 {
        fn square(&self) -> Self {
            self * self
        }
    }

    assert_eq!(42i32.square(), 42 * 42);
}

#[test]
fn type_bounds() {
    trait LendingIterator {
        #[bounds(Self: 'a)]
        type Item<'a>;

        fn next(&mut self) -> Option<Self::Item<'_>>;
    }

    struct WindowsMut<'t, T> {
        slice: &'t mut [T],
        cursor: usize,
        window_size: usize,
    }

    impl<'t, T> LendingIterator for WindowsMut<'t, T> {
        #[bounds(Self: 'a)]
        type Item<'a> = &'a mut [T];

        fn next(&mut self) -> Option<Self::Item<'_>> {
            let window = self
                .slice
                .get_mut(self.cursor..self.cursor + self.window_size)?;
            self.cursor += 1;
            Some(window)
        }
    }

    let mut v = vec![1, 2, 3, 4, 5];
    let mut w = WindowsMut {
        slice: v.as_mut_slice(),
        cursor: 0,
        window_size: 3,
    };

    while let Some(w) = w.next() {
        for a in w.iter_mut() {
            *a += 1;
        }
    }
    assert_eq!(v, &[2, 4, 6, 6, 6]);
}

#[test]
fn union_bounds() {
    #[bounds(A: Copy)]
    #[bounds(B: Copy)]
    union Union<A, B> {
        a: A,
        b: B,
    }

    let _ = Union::<i32, u8> { a: 42 };
    let _ = Union::<i32, u8> { b: 255 };
}