How to assign string to *mut () type?

1

pub struct TraitObject {
pub data: *mut (),

}

fn main() {

let mut a: String = "foo".to_string();
let b = TraitObject { data: &mut a };
}

//how to assign string to traitobject data field..
//then how to call trait object data field as string

2

What are you actually trying to do?

3

Am trying to understand internals trait object

4

Is this what you are trying to do?

#[repr(C)]
#[derive(Debug)]
pub struct TraitObject {
    pub ptr: *mut (),
    pub extra: usize,
}

fn main() {
    let a: String = "foo".to_string();
    let ref_a: &str = a.as_str();
    
    let b: TraitObject = unsafe { std::mem::transmute(ref_a) };
    println!("{:?}", b);
}
5

Is this transmute guaranteed to be safe, however? What about alignment, for example?

6

The transmute is undefined behavior because the layout of fat pointers is not defined. There are no alignment issues.

7

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