Standard Library

The common vocabulary types include:

• types: used for optional values and error handling.

• : a hash map type with a configurable hashing algorithm.

• In fact, Rust contains several layers of the Standard Library: core, alloc and std.

• includes the most basic types and functions that don’t depend on libc, allocator or even the presence of an operating system.
• Embedded Rust applications often only use core, and sometimes alloc.