[slaymaker1907]

One big glaring flaw IMO is that it is not really possible to just turn off certain checks as opposed to turning them all off. For instance, maybe I need to call an unsafe C api or something but could still use the borrow checker.

[dbaupp]

An `unsafe` block only enables extra features, it doesn't change existing behaviour of safe Rust. Specifically, it allows calling `unsafe` functions (FFI and pure Rust `unsafe` ones), dereferencing raw pointers and some minor other stuff (e.g., inline assembly, some manipulations of packed structs). The borrow checker still works on references, the trait system still enforces Send/Sync for concurrency, and the type system still requires things to have matching types.

It's definitely true that having a one dimensional `unsafe` might seem unnecessarily powerful in some cases (e.g. an particular unsafe block might just need to do some pointer offsetting and dereferencing, but no FFI), but it isn't a "you're on your own" hammer.

[hashmal]

The Rust book clearly states:

"It’s important to understand that unsafe doesn’t turn off the borrow checker or disable any other of Rust’s safety checks" [1]

"unsafe" unlocks only 4 things: Dereferencing a raw pointer, Calling an unsafe function or method, Accessing or modifying a mutable static variable, Implementing an unsafe trait.

[1] https://doc.rust-lang.org/book/second-edition/ch19-01-unsafe...

[burntsushi]

In Rust, the borrow checker is still enabled in unsafe blocks.