$ cargo run
   Compiling iterators v0.1.0 (file:///projects/iterators)
warning: unused `Map` that must be used
 --> src/main.rs:4:5
  |
4 |     v1.iter().map(|x| x + 1);
  |     ^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: iterators are lazy and do nothing unless consumed
  = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
  |
4 |     let _ = v1.iter().map(|x| x + 1);
  |     +++++++

warning: `iterators` (bin "iterators") generated 1 warning
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.47s
     Running `target/debug/iterators`