From a9aa2dfe844840a7e414873ce55ef9d02f1038a7 Mon Sep 17 00:00:00 2001 From: Guillaume Gomez Date: Sun, 19 Jan 2020 15:35:55 +0100 Subject: [PATCH] clean up E0204 explanation --- src/librustc_error_codes/error_codes/E0204.md | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/src/librustc_error_codes/error_codes/E0204.md b/src/librustc_error_codes/error_codes/E0204.md index 315690111359..96e44758be4f 100644 --- a/src/librustc_error_codes/error_codes/E0204.md +++ b/src/librustc_error_codes/error_codes/E0204.md @@ -1,21 +1,24 @@ -An attempt to implement the `Copy` trait for a struct failed because one of the -fields does not implement `Copy`. To fix this, you must implement `Copy` for the -mentioned field. Note that this may not be possible, as in the example of +The `Copy` trait was implemented on a type which contains a field that doesn't +implement the `Copy` trait. + +Erroneous code example: ```compile_fail,E0204 struct Foo { - foo : Vec, + foo: Vec, } -impl Copy for Foo { } +impl Copy for Foo { } // error! ``` -This fails because `Vec` does not implement `Copy` for any `T`. +The `Copy` trait is implemented by default only on primitive types. If your +type only contains primitive types, you'll be able to implement `Copy` on it. +Otherwise, it won't be possible. Here's another example that will fail: ```compile_fail,E0204 -#[derive(Copy)] +#[derive(Copy)] // error! struct Foo<'a> { ty: &'a mut bool, }