README.md

Struct Usage

To print a struct it needs to implement the std::fmt::Display and std::fmt::Debug trait. This gives the user control over how/what to print from the struct. To use the default/dev friendly output of all members use the {:?} or {:#?} format specifiers after the struct specifies the outer attribute of #[derive(Debug)].

To get rid of the error add the #[derive(Debug)] attribute.

= help: the trait `Debug` is not implemented for `Rectangle`
= note: add `#[derive(Debug)]` to `Rectangle` or manually `impl Debug for Rectangle`

#[derive(Debug)]
struct Rectangle {
    width: u32,
    height: u32,
}

fn main() {

    let mut r = Rectangle {
        height: 36,
        width: 24,
    };
   println!("{:#?}", r);
   ...

Debug Macro

dbg! macro can be used to print values to stderr. The macro takes ownership and returns it back. In order to receive a value back into the variable it needs to be mutable.

fn main() {
    let mut r = Rectangle {
        height: 36,
        width: 24,
    };
    // dbg! macro can be used to print values to stderr
    // The macro takes ownership and returns it back.

    r = dbg!(r);

    // or a reference could be passed into

    // dbg(&r);

    //    println!("{:#?}", r);
    dbg!("Area: {}", area(&r));
}