rustlings/exercises/standard_library_types/README.md

For the Box exercise check out the chapter Using Box to Point to Data on the Heap.

For the Arc exercise check out the chapter Shared-State Concurrency of the Rust Book.

For the Iterator exercise check out the chapters Iterator of the Rust Book and the Iterator documentation. Do not adjust your monitors-- iterators1.rs is indeed missing. Iterators is a challenging topic, so we're leaving space for a simpler exercise!