| // Copyright 2014 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| #![doc(primitive = "unit")] |
| #![stable(feature = "rust1", since = "1.0.0")] |
| |
| //! The `()` type, sometimes called "unit" or "nil". |
| //! |
| //! The `()` type has exactly one value `()`, and is used when there |
| //! is no other meaningful value that could be returned. `()` is most |
| //! commonly seen implicitly: functions without a `-> ...` implicitly |
| //! have return type `()`, that is, these are equivalent: |
| //! |
| //! ```rust |
| //! fn long() -> () {} |
| //! |
| //! fn short() {} |
| //! ``` |
| //! |
| //! The semicolon `;` can be used to discard the result of an |
| //! expression at the end of a block, making the expression (and thus |
| //! the block) evaluate to `()`. For example, |
| //! |
| //! ```rust |
| //! fn returns_i64() -> i64 { |
| //! 1i64 |
| //! } |
| //! fn returns_unit() { |
| //! 1i64; |
| //! } |
| //! |
| //! let is_i64 = { |
| //! returns_i64() |
| //! }; |
| //! let is_unit = { |
| //! returns_i64(); |
| //! }; |
| //! ``` |
