Function boxed_deleter 

pub unsafe fn boxed_deleter<T: ?Sized>(ptr: *mut T)

Default Rust deleter.

Invokes destructor and de-allocates memory using global allocator, using Box.

It can be useful when one would want to allow type erasure, but it is UB to specify invalid T

use smart_ptr::Unique;

let var = Box::new("test".to_string());
unsafe {
    smart_ptr::boxed_deleter::<String>(Box::leak(var) as *mut String);
}

Warning

Remember that things can get complicated when you cast from fat ptrs(with vtable)