Error code E0756
The ffi_const
attribute was used on something other than a foreign function
declaration.
Erroneous code example:
#![feature(ffi_const)] #[ffi_const] // error! pub fn foo() {} fn main() {}
The ffi_const
attribute can only be used on foreign function declarations
which have no side effects except for their return value:
#![feature(ffi_const)] extern "C" { #[ffi_const] // ok! pub fn strlen(s: *const i8) -> i32; } fn main() {}
You can get more information about it in the unstable Rust Book.