autoderef-box-no-add.rs

//! Tests that auto-dereferencing does not allow addition of `Box<isize>` values.
//!
//! This test ensures that `Box<isize>` fields in structs (`Clam` and `Fish`) are not
//! automatically dereferenced to `isize` during addition operations, as `Box<isize>`
//! does not implement the `Add` trait.

struct Clam {
    x: Box<isize>,
    y: Box<isize>,
}

struct Fish {
    a: Box<isize>,
}

fn main() {
    let a: Clam = Clam {
        x: Box::new(1),
        y: Box::new(2),
    };
    let b: Clam = Clam {
        x: Box::new(10),
        y: Box::new(20),
    };
    let z: isize = a.x + b.y;
    //~^ ERROR cannot add `Box<isize>` to `Box<isize>`
    println!("{}", z);
    assert_eq!(z, 21);
    let forty: Fish = Fish { a: Box::new(40) };
    let two: Fish = Fish { a: Box::new(2) };
    let answer: isize = forty.a + two.a;
    //~^ ERROR cannot add `Box<isize>` to `Box<isize>`
    println!("{}", answer);
    assert_eq!(answer, 42);
}