Rust 語言學習之旅（2）

#![allow(dead_code)] // this line prevents compiler warnings

enum Species {
    Crab,
    Octopus,
    Fish,
    Clam
}

struct SeaCreature {
    species: Species,
    name: String,
    arms: i32,
    legs: i32,
    weapon: String,
}

fn main() {
    let ferris = SeaCreature {
        species: Species::Crab,
        name: String::from("Ferris"),
        arms: 2,
        legs: 4,
        weapon: String::from("claw"),
    };

    match ferris.species {
        Species::Crab => println!("{} is a crab",ferris.name),
        Species::Octopus => println!("{} is a octopus",ferris.name),
        Species::Fish => println!("{} is a fish",ferris.name),
        Species::Clam => println!("{} is a clam",ferris.name),
    }
}

#![allow(dead_code)] // this line prevents compiler warnings

enum Species { Crab, Octopus, Fish, Clam }
enum PoisonType { Acidic, Painful, Lethal }
enum Size { Big, Small }
enum Weapon {
    Claw(i32, Size),
    Poison(PoisonType),
    None
}

struct SeaCreature {
    species: Species,
    name: String,
    arms: i32,
    legs: i32,
    weapon: Weapon,
}

fn main() {
    // SeaCreature's data is on stack
    let ferris = SeaCreature {
        // String struct is also on stack,
        // but holds a reference to data on heap
        species: Species::Crab,
        name: String::from("Ferris"),
        arms: 2,
        legs: 4,
        weapon: Weapon::Claw(2, Size::Small),
    };

    match ferris.species {
        Species::Crab => {
            match ferris.weapon {
                Weapon::Claw(num_claws,size) => {
                    let size_description = match size {
                        Size::Big => "big",
                        Size::Small => "small"
                    };
                    println!("ferris is a crab with {} {} claws", num_claws, size_description)
                },
                _ => println!("ferris is a crab with some other weapon")
            }
        },
        _ => println!("ferris is some other animal"),
    }
}

// 一個部分定義的結構體型別
struct BagOfHolding<T> {
    item: T,
}

fn main() {
    // 注意：透過使用泛型，我們建立了編譯時才建立的型別，使程式碼更大
    // Turbofish 使之顯式化
    let i32_bag = BagOfHolding::<i32> { item: 42 };
    let bool_bag = BagOfHolding::<bool> { item: true };
    
    // Rust 也可以推斷出泛型的型別！
    let float_bag = BagOfHolding { item: 3.14 };

    // 注意：在現實生活中，不要把一袋東西放在另一袋東西里:)
    let bag_in_bag = BagOfHolding {
        item: BagOfHolding { item: "嘭！" },
    };

    println!(
        "{} {} {} {}",
        i32_bag.item, bool_bag.item, float_bag.item, bag_in_bag.item.item
    );
}

enum Item {
    Inventory(String),
    // None represents the absence of an item
    None,
}

struct BagOfHolding {
    item: Item,
}

enum Option<T> {
    None,
    Some(T),
}

fn do_something_that_might_fail(i: i32) -> Result<f32, String> {
    if i == 42 {
        Ok(13.0)
    } else {
        Err(String::from("this is not the right number"))
    }
}

// 主函式不返回值，但可能返回一個錯誤！
fn main() -> Result<(), String> {
    let result = do_something_that_might_fail(12);

    match result {
        Ok(v) => println!("found {}", v),
        Err(_e) => {
            // 優雅地處理錯誤
            
            // 返回一個說明發生了什麼的新錯誤！
            return Err(String::from("something went wrong in main!"));
        }
    }

   // 注意我們在 Result Ok 中使用了一個單位值
     // 表示一切都很好
    Ok(())
}

do_something_that_might_fail()?
match do_something_that_might_fail() {
    Ok(v) => v,
    Err(e) => return Err(e),
}

fn main() {
    // 我們可以顯式確定型別
    let mut i32_vec = Vec::<i32>::new(); // turbofish <3
    i32_vec.push(1);
    i32_vec.push(2);
    i32_vec.push(3);

    // 但是看看 Rust 是多麼聰明的自動檢測型別啊
    let mut float_vec = Vec::new();
    float_vec.push(1.3);
    float_vec.push(2.3);
    float_vec.push(3.4);

    // 這是個漂亮的宏！
    let string_vec = vec![String::from("Hello"), String::from("World")];

    for word in string_vec.iter() {
        println!("{}", word);
    }
}