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#![feature(unboxed_closures, fn_traits)] | |
fn main() { | |
let add = |a: i32, b: i32| a + b; | |
let sqr = |a: i32| a.pow(2); | |
let add_two = |a: i32| a + 2; | |
assert_eq!(chain(add, sqr)(2, 3), 25); | |
assert_eq!( | |
chain( | |
chain( | |
chain(add_two, sqr), | |
add_two | |
), | |
add_two | |
)(2), 20); | |
assert_eq!(chain(sqr, sqr)(2), 16); | |
} | |
pub struct Chain<F, G>(F, G); | |
impl<F, G> Chain<F, G> { | |
fn new<A, B, C>(f: F, g: G) -> Self where | |
F: FnOnce<A, Output = B>, | |
G: FnOnce<(B,), Output = C>, | |
{ | |
Chain(f, g) | |
} | |
} | |
impl<A, B, C, F, G> FnOnce<A> for Chain<F, G> | |
where | |
F: FnOnce<A, Output = B>, | |
G: FnOnce<(B,), Output = C>, | |
{ | |
type Output = C; | |
extern "rust-call" fn call_once(self, args: A) -> Self::Output { | |
let Chain(f1, f2) = self; | |
f2.call_once((f1.call_once(args),)) | |
} | |
} | |
fn chain<A, B, C, F, G>(f: F, g: G) -> impl FnOnce<A, Output = C> | |
where | |
F: FnOnce<A, Output = B>, | |
G: FnOnce<(B,), Output = C>, | |
{ | |
Chain::new(f, g) | |
} |
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