Macro prt! to explore memory allocation

---

examples/macros/macro-prt/src/main.rs

macro_rules! prt {
    ($var:expr) => {
        println!(
            "{:2} {:2} {:p} {:15?} '{}'",
            $var.len(),
            $var.capacity(),
            &$var,
            $var.as_ptr(),
            $var
        );
    };
}

fn main() {
    let string1 = String::from("Rust");
    prt!(string1);
}

 4  4 0x7ffd119a2c90  0x57b54274fb80 'Rust'