Rust Essentials - Second Edition

When is code unsafe

There are situations in which even the Rust compiler cannot guarantee that our code will behave in a safe manner. This could occur when:

• We need to program against the metal, close to the operating system, processors, and hardware
• We want to work with the same amount of control as is possible in C
• We delegate a part of the program execution to an unsafe language, such as C
• We want to use inline assembly language

Rust allows us to do all of these, but we have to envelop this possibly dangerous code in an unsafe block:

       unsafe {
         // possibly dangerous code
       }  

This means that the programmer takes full responsibility for the code in the block. The unsafe block is a promise to the compiler that the danger does not leak ...