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#![allow(unused_imports)] #[cfg(feature = "proc-macro")] pub use indirect_once_derive::*; #[cfg(not(feature = "parking-lot"))] use std::sync::Once; #[cfg(feature = "parking-lot")] use parking_lot::Once; #[macro_export] macro_rules! indirect_fn { (resolver = $resolver: ident ; fn $name:ident($($arg: ident : $pty: ty),*) {}) => { $crate::indirect_fn!(resolver = $resolver; fn $name($($arg: $pty),*) -> () {})}; (resolver = $resolver: ident ; fn $name:ident($($arg: ident : $pty: ty),*) -> $ret: ty {})=> { fn $name($($arg: $pty),*) -> $ret { static mut IMPL: Option<&'static fn($($pty),*) -> $ret> = None; static INIT: Once = Once::new(); unsafe { INIT.call_once(|| { IMPL = Some($resolver()); }); (IMPL.unwrap())($($arg),*) } } } } #[cfg(test)] mod tests { use super::*; fn incr(x: i32) -> i32 { x + 1 } fn decr(x: i32) -> i32 { x - 1 } fn foo() -> &'static fn(i32) -> i32 { &(incr as fn(i32) -> i32) } fn bar() -> &'static fn(i32) -> i32 { &(decr as fn(i32) -> i32) } #[test] #[cfg(feature = "proc-macro")] fn it_works() { #[indirect(resolver = "foo")] fn hello_world(arg: i32) -> i32 {} assert_eq!(hello_world(10), 11); } #[test] #[cfg(feature = "proc-macro")] fn it_works_2() { #[indirect(resolver = "bar")] fn hello_hello(arg: i32) -> i32 {} assert_eq!(hello_hello(10), 9); } #[test] #[cfg(feature = "proc-macro")] fn multiple_arguments() { fn do_thingy(one: i32, two: i32, really: bool) -> (bool, i32) { if really { (really, one + two) } else { (really, two) } } fn pick() -> &'static fn(i32, i32, bool) -> (bool, i32) { &(do_thingy as _) } #[indirect(resolver = "pick")] fn foo(one: i32, two: i32, three: bool) -> (bool, i32) {} assert_eq!(foo(1, 2, true), (true, 3)) } #[test] fn macro_impl() { indirect_fn! { resolver = foo; fn dog(param: i32) -> i32 {} } assert_eq!(dog(41), 42); } }