Shared via Rust Playground

playground.rs

struct StructNoLifetime {}
impl StructNoLifetime {
    pub fn do_nothing(&mut self) {
    }
}
struct StructWithLifetime <'a> {
    pub field: &'a i32
}

fn main() {

    let mut some_val = StructNoLifetime{};
    some_val.do_nothing();
    borrow_mut_function(&mut some_val);
    borrow_mut_function(&mut some_val);
    
    let num = 5;
    let mut life_val = StructWithLifetime{field:&num};
    borrow_lifetime(&mut life_val);
    borrow_lifetime(&mut life_val);
    let num_again = borrow_lifetime(&mut life_val);
    borrow_lifetime(&mut life_val);
}

fn borrow_mut_function(val_in: &mut StructNoLifetime) -> String {
    "abc".to_string()
}

fn borrow_lifetime<'a>(val_in: &'a mut StructWithLifetime) -> &'a i32 {
    val_in.field
}