ugly.rs

use std::mem;
use std::ptr;
use std::sync::Arc;
use std::collections::HashMap;


fn main() {
    let mut hm = HashMap::new();
    let key = (Arc::new("1".to_string()), Arc::new("2".to_string()));
    let data = vec![key.0.clone(), key.1.clone()];
    hm.insert(key, 42);

    unsafe {
        let mut stack_key: (Arc<String>, Arc<String>) = mem::uninitialized();
        ptr::copy_nonoverlapping(&data[0] as *const Arc<String>, &mut stack_key.0 as *mut Arc<String>, mem::size_of::<Arc<String>>());
        ptr::copy_nonoverlapping(&data[1] as *const Arc<String>, &mut stack_key.1 as *mut Arc<String>, mem::size_of::<Arc<String>>());
        println!("lookup result: {}", hm[&stack_key]);
        mem::forget(stack_key);
    }
}

For those that come across this through whatever magical means, note that the third argument to ptr::copy_nonoverlapping is count, not size. So the last argument to both those calls should be 1, not mem::size_of::<T>(). See also mit-pdos/noria@36b3485.