47 wiersze
1.2 KiB
Rust
47 wiersze
1.2 KiB
Rust
//-- #########################
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//-- Task: Implementing and_then
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//-- Author: Vigneshwer.D
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//-- Version: 1.0.0
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//-- Date: 26 March 17
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//-- #########################
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#![allow(dead_code)]
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#[derive(Debug)] enum Food { CordonBleu, Steak, Sushi }
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#[derive(Debug)] enum Day { Monday, Tuesday, Wednesday }
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// We don't have the ingredients to make Sushi.
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fn have_ingredients(food: Food) -> Option<Food> {
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match food {
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Food::Sushi => None,
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_ => Some(food),
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}
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}
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// We have the recipe for everything except Cordon Bleu.
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fn have_recipe(food: Food) -> Option<Food> {
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match food {
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Food::CordonBleu => None,
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_ => Some(food),
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}
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}
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// This can conveniently be rewritten more compactly with `and_then()`:
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fn cookable(food: Food) -> Option<Food> {
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have_ingredients(food).and_then(have_recipe)
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}
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fn eat(food: Food, day: Day) {
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match cookable(food) {
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Some(food) => println!("Yay! On {:?} we get to eat {:?}.", day, food),
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None => println!("Oh no. We don't get to eat on {:?}?", day),
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}
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}
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fn main() {
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let (cordon_bleu, steak, sushi) = (Food::CordonBleu, Food::Steak, Food::Sushi);
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eat(cordon_bleu, Day::Monday);
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eat(steak, Day::Tuesday);
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eat(sushi, Day::Wednesday);
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} |