pin experiments

Author: cfsamson

ch10/x-pin-experiments/Cargo.toml

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+[package]
+name = "x-pin-experiments"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+rand = "0.8.5"

ch10/x-pin-experiments/src/main.rs

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+use rand::prelude::*;
+
+fn main() {
+    selfref1();
+}
+
+fn selfref1() {
+    let mut first = SelfRef1::new(0);
+    println!("It's OK: {}", first.b());
+    let second = std::mem::replace(first.as_mut(), *SelfRef1::new(2));
+    println!("Ooops: {}", first.b());
+    println!("Ooops: {}", second.b());
+}
+
+#[derive(Debug)]
+struct SelfRef1 {
+    a: [char;3],
+    b: *const char,
+}
+
+impl SelfRef1 {
+    fn new(n: usize) -> Box<Self> {
+        let mut selfref = Box::new(Self {
+            a: ['a', 'b', 'c'],
+            b: std::ptr::null(),
+        });
+        selfref.b = &selfref.a[n] as *const _;
+        selfref
+    }
+
+    fn b(&self) -> &char {
+        unsafe { &*self.b }
+    }
+}
+
+// =======================================================
+use std::pin::Pin;
+
+fn selfref2() {
+    let mut first = SelfRef2::new(0);
+    println!("It's OK: {}", first.b());
+    let mut second = SelfRef2::new(2);
+    std::mem::swap(&mut first, &mut second);
+    println!("Ooops: {}", first.b());
+}
+
+#[derive(Debug)]
+struct SelfRef2 {
+    a: [char;3],
+    b: *const char,
+    _pin: std::marker::PhantomPinned,
+}
+
+impl SelfRef2 {
+    fn new(n: usize) -> Pin<Box<Self>> {
+        let mut selfref = Box::pin(Self {
+            a: ['a', 'b', 'c'],
+            b: std::ptr::null(),
+            _pin: std::marker::PhantomPinned,
+        });
+        //selfref.b = &selfref.a[n] as *const _;
+        selfref
+    }
+
+    fn b(&self) -> &char {
+        unsafe { &*self.b }
+    }
+}