Mutable Static docs (owned pointers / sync)

[mitaa]

static mut FOO: Option<Box<usize>> = None;
//<anon>:1:38: 1:42 error: mutable statics are not allowed to have owned pointers
//<anon>:1 static mut FOO: Option<Box<usize>> = None;
                                                ^~~~

I am not sure why this is forbidden, but it is certainly undocumented.

Also the TRPL says Furthermore, any type stored in a static must be Sync. but does not mention that this is not true for static mut's.

[steveklabnik]

whoah, we still have 'owned pointers' in an error message?

[nham]

@steveklabnik I'm planning on tackling this by adding an error code and an explanation. What do you think the error message should be instead? mutable statics are not allowed to have boxes ?

[steveklabnik]

Yes, thanks!

[steveklabnik]

This error now says 'hello.rs:1:38: 1:42 error: mutable statics are not allowed to have boxes [E0397]' on nightly

[nham]

Yes, however the "explanation" is still lacking I think. It just says

It is not allowed for a mutable static to allocate or have destructors.

Not really an explanation ;) Also, RFC 246, which introduced this error, doesn't discuss this topic from what I read, so I'm not exactly sure why this is disallowed.