update

technology/dev/programming/languages/Rust.md

@@ -620,6 +620,28 @@ mymacro!("Hello", "World");
 
 This macro gets expanded to the code inside the `macro_rules!` section with the provided arguments. For more information on macros, see the [docs](https://doc.rust-lang.org/reference/macros-by-example.html).
 
+## `unsafe` Rust
+Rust is focused strongly on safety, but sometimes doing something dangerous is necessary. In this case you can use the `unsafe` keyword. `unsafe` should be used only when needed as it may cause undefinied behaviour, but when debugging you can solely focus on your `unsafe` blocks as all potential dangerous operations are neatly packaged in them.
+
+There are two types of using `unsafe`:
+- `unsafe` blocks lets you call dangerous code. With this you can wrap unsafe code in a safe function with checks to call.
+```rust
+fn write_to_serial(data: &[u8]) {
+    assert!(data.is_valid());
+
+    unsafe {
+        // doing potentially unsafe things
+        write_to_serial_unchecked(data);
+    }
+}
+```
+- `unsafe` functions can only be called from `unsafe` blocks.
+```rust
+unsafe fn write_to_serial_unchecked(data: &[u8]) {
+    // unsafe operation
+}
+```
+
 ## [Crates](https://lib.rs/)
 - [anyhow](https://lib.rs/crates/anyhow): Flexible concrete Error type built on `std::error::Error`
 - [itertools](https://lib.rs/crates/itertools): Extra iterator adaptors, iterator methods, free functions, and macros