diff --git a/src/doc/trpl/closures.md b/src/doc/trpl/closures.md index 4479fdb7baa..428897821cf 100644 --- a/src/doc/trpl/closures.md +++ b/src/doc/trpl/closures.md @@ -324,37 +324,34 @@ first, it may seem strange, but we’ll figure it out. Here’s how you’d prob try to return a closure from a function: ```rust,ignore -fn factory() -> (Fn(i32) -> Vec) { - let vec = vec![1, 2, 3]; +fn factory() -> (Fn(i32) -> i32) { + let num = 5; - |n| vec.push(n) + |x| x + num } let f = factory(); -let answer = f(4); -assert_eq!(vec![1, 2, 3, 4], answer); +let answer = f(1); +assert_eq!(6, answer); ``` This gives us these long, related errors: ```text error: the trait `core::marker::Sized` is not implemented for the type -`core::ops::Fn(i32) -> collections::vec::Vec` [E0277] -f = factory(); -^ -note: `core::ops::Fn(i32) -> collections::vec::Vec` does not have a -constant size known at compile-time -f = factory(); -^ -error: the trait `core::marker::Sized` is not implemented for the type -`core::ops::Fn(i32) -> collections::vec::Vec` [E0277] -factory() -> (Fn(i32) -> Vec) { - ^~~~~~~~~~~~~~~~~~~~~ -note: `core::ops::Fn(i32) -> collections::vec::Vec` does not have a constant size known at compile-time -factory() -> (Fn(i32) -> Vec) { - ^~~~~~~~~~~~~~~~~~~~~ - +`core::ops::Fn(i32) -> i32` [E0277] +fn factory() -> (Fn(i32) -> i32) { + ^~~~~~~~~~~~~~~~ +note: `core::ops::Fn(i32) -> i32` does not have a constant size known at compile-time +fn factory() -> (Fn(i32) -> i32) { + ^~~~~~~~~~~~~~~~ +error: the trait `core::marker::Sized` is not implemented for the type `core::ops::Fn(i32) -> i32` [E0277] +let f = factory(); + ^ +note: `core::ops::Fn(i32) -> i32` does not have a constant size known at compile-time +let f = factory(); + ^ ``` In order to return something from a function, Rust needs to know what @@ -364,16 +361,16 @@ way to give something a size is to take a reference to it, as references have a known size. So we’d write this: ```rust,ignore -fn factory() -> &(Fn(i32) -> Vec) { - let vec = vec![1, 2, 3]; +fn factory() -> &(Fn(i32) -> i32) { + let num = 5; - |n| vec.push(n) + |x| x + num } let f = factory(); -let answer = f(4); -assert_eq!(vec![1, 2, 3, 4], answer); +let answer = f(1); +assert_eq!(6, answer); ``` But we get another error: @@ -448,7 +445,8 @@ assert_eq!(6, answer); We use a trait object, by `Box`ing up the `Fn`. There’s just one last problem: ```text -error: `num` does not live long enough +error: closure may outlive the current function, but it borrows `num`, +which is owned by the current function [E0373] Box::new(|x| x + num) ^~~~~~~~~~~ ```