public/subjects/question_mark

question_mark

Instructions

Create the following structures. Each has one element:

• One: first_layer as type Option<Two>.
• Two: second_layer as type Option<Three>
• Three: third_layer as type Option<Four>
• Four: fourth_layer as type Option<u16>.

Beside the structures, you must create a function named get_fourth_layer, and associate it to the One structure. This function should return the Option value in the Four structure.

Expected Function and structures

pub struct One {
    // expected public fields
}
pub struct Two {
    // expected public fields
}
pub struct Three {
    // expected public fields
}
pub struct Four {
    // expected public fields
}

impl One {
    pub fn get_fourth_layer(&self) -> Option<u16> {}
}

Usage

Here is a program to test your function:

use question_mark::*;

fn main() {
    let a = One {
        first_layer : Some(Two {
            second_layer: Some(Three {
                third_layer: Some(Four {
                    fourth_layer: Some(1000)
                })
            })
        })
    };

    // output: 1000
    println!("{:?}", match a.get_fourth_layer() {
        Some(e) => e,
        None => 0
    })
}

And its output:

$ cargo run
1000
$

Notions

• Unpacking options with ?