Why is three safety levels need in D?

[Stefan Koch via Digitalmars-d-learn]

On Thursday, 17 November 2016 at 17:18:27 UTC, Nordlöw wrote:
> Why does D need both `@safe`, `@trusted` and `@system` when 
> Rust seems to get by with only safe (default) and `unsafe`?
>
> https://dlang.org/spec/memory-safe-d.html
> http://dlang.org/safed.html

It allows encapsulating unsafe operations in safely-callable 
wrappers.