“A fundamental principle of Rust code is that it is sound.

“We’ll create a formal definition of the term soundness shortly. In the meantime, think of sound code as code that cannot trigger memory safety problems.

“Sound code is made up of sound functions and sound operations.

“A sound function is a function where none of its possible inputs could provoke soundness problems.

Sound functions have common shapes.

Those shapes are what we’ll look at now.

“We’ll start with one that’s implemented in Safe Rust, and then see what could happen when we introduce unsafe to different parts.