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Clean up E0764 explanation

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Guillaume Gomez 2020-08-31 20:14:37 +02:00
parent 6c44bcc4ff
commit 153f966d00
1 changed files with 13 additions and 9 deletions
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22
compiler/rustc_error_codes/src/error_codes/E0764.md
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@ -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: