forget and drop functions

Below are the signatures for the drop() and forget() functions:

#![allow(unused)]
fn main() {
// std::mem::forget
fn forget<T>(t: T) {
    let _ = std::mem::ManuallyDrop::new(t);
}

// std::mem::drop
fn drop<T>(_x: T) {}
}

  • Both mem::forget() and mem::drop() take ownership of the value t.

  • Despite having the same function signature, they have opposite effects:

    • forget() uses ManuallyDrop to prevent the destructor Drop::drop() from being invoked.

      This is useful for scenarios such as implementing a drop bomb or otherwise opting out of destructor behavior.

      Be careful though, since any resources the value exclusively owns such as heap allocated memory or file handles will remain in an unreachable state.

    • drop() is a convenience function for disposing of a value. Because t is moved into the function, it is automatically dropped which triggers its Drop::drop() implementation before the parent function returns.