Don't use transmute!

[steveklabnik]

Hey there! I wanted to send you a PR, but couldn't find the text of the gitbook, so I'll just open an issue.

in https://davidmcneil.gitbooks.io/the-rusty-web/content/counter-example.html

this code is better written as

#[no_mangle]
unsafe pub extern "C" fn counter_destroy(counter: *mut Counter) {
    Box::from_raw(counter)
}

#[no_mangle]
pub extern "C" fn counter_create() -> *mut Counter {
    Box::into_raw(Box::new(Counter::new()))
}

That is, from_raw/into_raw over transmute, and the unsafety only belongs on counter_destroy; if you did a null check inside of it, you could make it safe too.

Very interesting guide, thanks for sharing it!

[davidMcneil]

Thank you for the feedback! That is a much better method.

And thank you for all you do in the Rust community. The books specifically are amazing!