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Add helpful hint in io docs about how ? is not allowed in main() #40763

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Apr 1, 2017
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12 changes: 12 additions & 0 deletions src/libstd/io/mod.rs
Original file line number Diff line number Diff line change
Expand Up @@ -145,6 +145,18 @@
//! # }
//! ```
//!
//! Note that you cannot use the `?` operator in functions that do not return
//! a `Result<T, E>` (e.g. `main`). Instead, you can call `.unwrap()` or `match`
//! on the return value to catch any possible errors:
//!
//! ```
//! use std::io;
//!
//! let mut input = String::new();
//!
//! io::stdin().read_line(&mut input).unwrap();
//! ```
//!
//! And a very common source of output is standard output:
//!
//! ```
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