| // Copyright 2015 The Rust Project Developers. See the COPYRIGHT |
| // file at the top-level directory of this distribution and at |
| // http://rust-lang.org/COPYRIGHT. |
| // |
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| // option. This file may not be copied, modified, or distributed |
| // except according to those terms. |
| |
| |
| use std::mem; |
| |
| pub fn main() { |
| // By Ref Capture |
| let a = 10i32; |
| let b = Some(|| println!("{}", a)); |
| // When we capture by reference we can use any of the |
| // captures as the discriminant since they're all |
| // behind a pointer. |
| assert_eq!(mem::size_of_val(&b), mem::size_of::<usize>()); |
| |
| // By Value Capture |
| let a = Box::new(12i32); |
| let b = Some(move || println!("{}", a)); |
| // We captured `a` by value and since it's a `Box` we can use it |
| // as the discriminant. |
| assert_eq!(mem::size_of_val(&b), mem::size_of::<Box<i32>>()); |
| |
| // By Value Capture - Transitive case |
| let a = "Hello".to_string(); // String -> Vec -> Unique -> NonZero |
| let b = Some(move || println!("{}", a)); |
| // We captured `a` by value and since down the chain it contains |
| // a `NonZero` field, we can use it as the discriminant. |
| assert_eq!(mem::size_of_val(&b), mem::size_of::<String>()); |
| |
| // By Value - No Optimization |
| let a = 14i32; |
| let b = Some(move || println!("{}", a)); |
| // We captured `a` by value but we can't use it as the discriminant |
| // thus we end up with an extra field for the discriminant |
| assert_eq!(mem::size_of_val(&b), mem::size_of::<(i32, i32)>()); |
| } |