From 153f966d00b7e7f580ebc399a15e1f4c9115da65 Mon Sep 17 00:00:00 2001 From: Guillaume Gomez Date: Mon, 31 Aug 2020 20:14:37 +0200 Subject: [PATCH] Clean up E0764 explanation --- .../src/error_codes/E0764.md | 22 +++++++++++-------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/compiler/rustc_error_codes/src/error_codes/E0764.md b/compiler/rustc_error_codes/src/error_codes/E0764.md index e9061f988ac..0a2e2290e77 100644 --- a/compiler/rustc_error_codes/src/error_codes/E0764.md +++ b/compiler/rustc_error_codes/src/error_codes/E0764.md @@ -1,12 +1,4 @@ -Mutable references (`&mut`) can only be used in constant functions, not statics -or constants. This limitation exists to prevent the creation of constants that -have a mutable reference in their final value. If you had a constant of `&mut -i32` type, you could modify the value through that reference, making the -constant essentially mutable. While there could be a more fine-grained scheme -in the future that allows mutable references if they are not "leaked" to the -final value, a more conservative approach was chosen for now. `const fn` do not -have this problem, as the borrow checker will prevent the `const fn` from -returning new mutable references. +A mutable reference was used in a constant. Erroneous code example: @@ -19,6 +11,18 @@ fn main() { } ``` +Mutable references (`&mut`) can only be used in constant functions, not statics +or constants. This limitation exists to prevent the creation of constants that +have a mutable reference in their final value. If you had a constant of +`&mut i32` type, you could modify the value through that reference, making the +constant essentially mutable. + +While there could be a more fine-grained scheme in the future that allows +mutable references if they are not "leaked" to the final value, a more +conservative approach was chosen for now. `const fn` do not have this problem, +as the borrow checker will prevent the `const fn` from returning new mutable +references. + Remember: you cannot use a function call inside a constant or static. However, you can totally use it in constant functions: