Document some rust weird trick

lmumar · web-flow · commit fd4bc91a2b14 · 2018-01-26T17:41:13.000+08:00
Rust weird trick
diff --git a/_posts/2018-01-26-rust-trick.md b/_posts/2018-01-26-rust-trick.md
@@ -0,0 +1,51 @@
+---
+layout: post
+title: Weird Rust trick
+---
+
+### Weird Rust trick
+
+In Rust you cannot create another reference to a value if you already have a mutable reference to it. Example:
+```
+fn main() {
+    let mut x = 10;
+    let rx = &mut x;
+    *rx = 100;
+    
+    let irx = &x;
+    println!("irx={}", irx);
+}
+```
+If you compile this code you will receive the following errors:
+```
+   Compiling playground v0.0.1 (file:///playground)
+error[E0502]: cannot borrow `x` as immutable because it is also borrowed as mutable
+ --> src/main.rs:6:16
+  |
+3 |     let rx = &mut x;
+  |                   - mutable borrow occurs here
+...
+6 |     let irx = &x;
+  |                ^ immutable borrow occurs here
+...
+9 | }
+  | - mutable borrow ends here
+
+error: aborting due to previous error
+
+error: Could not compile `playground`.
+
+To learn more, run the command again with --verbose.
+```
+
+However you can trick the borrower checker by using a reference to a reference instead. So the code below will compile successfully in rust.
+```
+fn main() {
+    let mut x = 10;
+    let rx = &mut x;
+    *rx = 100;
+    
+    let irx = &rx;
+    println!("irx={}", irx);
+}
+```
