As with borrowing, we have to consider the scope to ensure that things work correctly.
The following piece of code, for example, won't work:
struct MyStruct<'a> {
lifea: &'a i32,
}
fn main()
{
let x;
{
let y = &5; // means let y = 5; let y = &y;
let f = MyStruct { lifea: y };
x = &f.lifea
}
println!("{}", x);
}
The code for this section is in the 08/lifetimescope folder of the supporting code bundle provided along with this book.
It may not seem obvious at first why this should not work. In terms of scope, f is created after y, so is in the scope of y and y is created within the scope of x. Or is it?
When the code is built, we will get the following output:
The error will be the x = &f.lifea, as we attempted to assign a value of something about to go out of scope.