Box

Box is an owned pointer to data on the heap:

1. fn main() {
2. let five = Box::new(5);
3. println!("five: {}", *five);
4. }

19.5. Box - 图1

Box<T> implements Deref<Target = T>, which means that you can call methods from T directly on a Box.

  • Box is like std::unique_ptr in C++.
  • In the above example, you can even leave out the * in the println! statement thanks to Deref.
  • A Box can be useful when you:
  • have a type whose size that can’t be known at compile time, but the Rust compiler wants to know an exact size.
  • want to transfer ownership of a large amount of data. To avoid copying large amounts of data on the stack, instead store the data on the heap in a Box so only the pointer is moved.