Preludes

Preludes là những thứ được định nghĩa trong std, và được import sẵn, vì chúng thường sẽ phải được dùng trong mọi chương trình Rust. Bạn có thể sử dụng mà không cần phải import, ví dụ như: Option, Result, Ok, Err, ...

Mặc dù std của Rust có rất nhiều module và tính năng, nhưng không phải mọi thứ đều được preludes.

Đây là danh sách những thứ được preludes: https://doc.rust-lang.org/std/prelude/#prelude-contents

• std::marker::{Copy, Send, Sized, Sync, Unpin}, marker traits that indicate fundamental properties of types.
• std::ops::{Drop, Fn, FnMut, FnOnce}, various operations for both destructors and overloading ().
• std::mem::drop, a convenience function for explicitly dropping a value.
• std::boxed::Box, a way to allocate values on the heap.
• std::borrow::ToOwned, the conversion trait that defines to_owned, the generic method for creating an owned type from a borrowed type.
• std::clone::Clone, the ubiquitous trait that defines clone, the method for producing a copy of a value.
• std::cmp::{PartialEq, PartialOrd, Eq, Ord}, the comparison traits, which implement the comparison operators and are often seen in trait bounds.
• std::convert::{AsRef, AsMut, Into, From}, generic conversions, used by savvy API authors to create overloaded methods.
• std::default::Default, types that have default values.
• std::iter::{Iterator, Extend, IntoIterator, DoubleEndedIterator, ExactSizeIterator}, iterators of various kinds.
• std::option::Option::{self, Some, None}, a type which expresses the presence or absence of a value. This type is so commonly used, its variants are also exported.
• std::result::Result::{self, Ok, Err}, a type for functions that may succeed or fail. Like Option, its variants are exported as well.
• std::string::{String, ToString}, heap-allocated strings.
• std::vec::Vec, a growable, heap-allocated vector.

The prelude used in Rust 2021, std::prelude::rust_2021, includes all of the above, and in addition re-exports:

• std::convert::{TryFrom, TryInto},
• std::iter::FromIterator.