What is `Box` and how is it different from `String` in Rust?(mahdi.blog)

    // heap-allocated, fixed-size
    struct BoxStr {
        unsigned length;
        // INVARIANT: this points to a heap allocation of length bytes, and is valid utf8
        unsigned char *data;
    }

    // heap-allocated, resizable
    struct String {
        unsigned length;
        unsigned capacity;
        // INVARIANT: heap allocation of capacity bytes, the first length of which are valid utf8
        unsigned char *data;
    }

    let boxed_str: Box<str> = "hello".into();
    println!("size of boxed_str on stack: {}", std::mem::size_of_val(&boxed_str));

    let s = String::from("hello!");
    println!("size of string on stack: {}", std::mem::size_of_val(&s));