Error code E0791
Static variables with the #[linkage]
attribute within external blocks
must have one of the following types, which are equivalent to a nullable
pointer in C:
-
*mut T
or*const T
, whereT
may be any type. -
An enumerator type with no
#[repr]
attribute and with two variants, where one of the variants has no fields, and the other has a single field of one of the following non-nullable types:- Reference type
- Function pointer type
The variants can appear in either order.
For example, the following declaration is invalid:
#![allow(unused)] #![feature(linkage)] fn main() { extern "C" { #[linkage = "extern_weak"] static foo: i8; } }
The following declarations are valid:
#![allow(unused)] #![feature(linkage)] fn main() { extern "C" { #[linkage = "extern_weak"] static foo: Option<unsafe extern "C" fn()>; #[linkage = "extern_weak"] static bar: Option<&'static i8>; #[linkage = "extern_weak"] static baz: *mut i8; } }