update rust

technology/dev/programming/languages/Rust.md

@@ -148,6 +148,13 @@ fn add_two(a: isize) -> isize {
 }
 ```
 
+The default return type of a function is the Unit Type `()`. You can also signal that a function will never return with `!`
+```rust
+fn infinity() -> ! {
+    loop {}
+}
+```
+
 ### Enums
 Rust has enums which can even hold some data.
 ```rust