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Error code E0755

The ffi_pure attribute was used on a non-foreign function.

Erroneous code example:

#![feature(ffi_pure)] #[unsafe(ffi_pure)] // error! pub fn foo() {} fn main() {}

The ffi_pure attribute can only be used on foreign functions which do not have side effects or infinite loops:

#![feature(ffi_pure)] extern "C" { #[unsafe(ffi_pure)] // ok! pub fn strlen(s: *const i8) -> isize; } fn main() {}

You can find more information about it in the unstable Rust Book.