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, where T 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; } }