不使用pin的话,在内存修改时可能会引发破坏自引用的问题。
如下是破坏自引用的代码
#[derive(Debug)]
struct Test {
a: String,
b: *const String,
}
impl Test {
fn new(txt: &str) -> Self {
Test {
a: String::from(txt),
b: std::ptr::null(),
}
}
fn init(&mut self) {
let self_ref: *const String = &self.a;
self.b = self_ref;
}
fn a(&self) -> &str {
&self.a
}
fn b(&self) -> &String {
assert!(!self.b.is_null(), "Test::b called without Test::init being called first");
unsafe { &*(self.b) }
}
}
fn main() {
let mut test1 = Test::new("test1");
test1.init();
let mut test2 = Test::new("test2");
test2.init();
println!("a: {}, b: {}", test1.a(), test1.b());
std::mem::swap(&mut test1, &mut test2);
println!("a: {}, b: {}", test2.a(), test2.b());
}