Crate expect

Expect

A flexible library for adding assertions to types.

#[derive(Default)]
struct Point {
    x: f64,
    y: f64
}

// Clockwise from the top left.
#[derive(Default)]
struct Square(Point, Point, Point, Point);

#[derive(Default)]
struct Contains(Point);

impl Assertion<Square> for Contains {
    fn assert(self, square: &Square) {
        assert!(self.0.x > square.0.x && self.0.x < square.1.x
             && self.0.y > square.2.y && self.0.y < square.1.y);
    }
}

let square = Square(
    Point { x: 0.0, y: 1.0 },
    Point { x: 1.0, y: 1.0 },
    Point { x: 1.0, y: 0.0 },
    Point { x: 0.0, y: 0.0 },
);

square
    .expect(Contains(Point { x: 0.5, y: 0.18 }))
    .expect(Contains(Point { x: 0.12, y: 0.9 }))

    // You can also use tuples of Assertions.
    .expect((Contains(Point { x: 0.63, y: 0.4 }),
             Contains(Point { x: 0.7, y: 0.85 })));

Traits

Assertion	An assertion that can be applied to a type.
Expect	Extension trait for applying assertions.