宏

声明宏

macro_rules! say_hello {
    () => {
        println!("Hello, Friends");
    };
    ($name:expr) => {
        println!("Hello, {}", $name);
    };
}

fn main() {
    say_hello!();
    say_hello!("John");
}

macro_rules! nameof {
    ($name:ident) => {
        stringify!($name)
    };
}

struct Person;

fn main() {
    println!("{}", nameof!(Person));
}

macro_rules! create_fn {
    ($name:ident, $body:expr) => {
        fn $name() -> i32 {
            $body
        }
    };
}

fn main() {
    create_fn!(get_one, 1);
    create_fn!(get_two, 2);

    println!("{}", get_one());
    println!("{}", get_two());
}

macro_rules! create_struct {
    ($name:ident, $($field_name:ident: $field_type:ty),*) => {
        #[derive(Debug)]
        struct $name {
            $($field_name: $field_type),*
        }

        impl $name {
            fn new($($field_name: $field_type),*) -> Self {
                Self {
                    $($field_name),*
                }
            }
        }
    };
}

fn main() {
    create_struct!(Person, name: String, age: i32);

    let person = Person::new(String::from("John"), 18);
    println!("person: {:#?}", person);
}

macro_rules! create_struct {
    ($name:ident, $($field_name:ident: $field_type:ty),*) => {
        #[derive(Debug)]
        struct $name {
            $($field_name: $field_type),*
        }

        impl $name {
            fn new($($field_name: $field_type),*) -> Self {
                Self {
                    $($field_name),*
                }
            }
        }
    };
}

fn main() {
    create_struct!(Person, name: String, age: i32);

    let person = Person::new(String::from("John"), 18);
    println!("person: {:#?}", person);
}

macro_rules! hashmap {
    ($($key:expr => $value:expr),* $(,)?) => {
        {
            use std::collections::HashMap;
            let mut map = HashMap::new();
            $(map.insert($key, $value);)*

            map
        }
    };
}

fn main() {
    let map = hashmap! (
        "a" => 1,
        "b" => 2,
        "c" => 3,
    );

    println!("map: {:#?}", map);
}

过程宏