You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: non_null_pointer.rs
    path of file: ./repos/tao-of-rust-codes/src/ch13
    
    the code of the file until where you have to start completion: /// # NonNull指针
///
/// `NonNull<T>`旨在成为`Unsafe Rust`默认的原生指针
/// 
/// Basic usage: NonNull内置方法展示
/// 
/// 允许开发者更安全地使用原生指针
///
/// ```rust
/// use std::ptr::{null, NonNull};
/// fn 
    
/// fn main() {
///    println!("*mut u64: {} bytes", mem::size_of::<*mut u64>());
///    println!("NonNull<*mut u64>: {} bytes", 
///        mem::size_of::<NonNull<*mut u64>>());
///    println!("Option<*mut u64>: {} bytes",
///        mem::size_of::<Option<*mut u64>>());
///    println!("Option<NonNull<*mut u64>>: {} bytes", 
///        mem::size_of::<Option<NonNull<*mut u64>>>());
///    println!("Option<Foo>: {} bytes",
///        mem::size_of::<Option<Foo>>());
///    println!("Option<FooUsingNonNull>: {} bytes",
///        mem::size_of::<Option<FooUsingNonNull>>());
/// }