←
Beta
Home

Now that we have an overview of how macros work, let's dive into another macro challenge. When implementing traits for multiple types, you often end up writing very similar code over and over.

In this challenge, you'll create a macro that generates implementations of a trait for multiple types. The goal is to reduce the amount of boilerplate code you need to write.

Your Task

  1. Write a macro named config_default_impl that:

    • Accepts a type and a default value as arguments.
    • Generates the implementation of ConfigDefault for that type.

  2. Use the macro to implement the ConfigDefault trait for the following types:

    • ConnectionTimeout with a value of 30.
    • MaxConnections with a value of 100.
    • RetryAttempts with a value of 3.
    • PostgresPort with a value of 5432.
    • MySQLPort with a value of 3306.
    • MongoPort with a value of 27017.
    • RedisPort with a value of 6379.

Hints

If you're stuck, feel free to check out the hints below:

<details> <summary>Click here to reveal hints</summary>

  • The syntax for a macro that accepts a type and a value is as follows:

    macro_rules! config_default_impl {
      ($type:ty, $value:expr) => {
          // Implementation here
      };
    }
</details>
← PreviousNext →
pub trait ConfigDefault {
    fn get_default() -> Self;
}


// These types need default values
pub struct ConnectionTimeout(pub u64);
pub struct MaxConnections(pub u32);
pub struct RetryAttempts(pub u8);
pub struct PostgresPort(pub u16);
pub struct MySQLPort(pub u16);
pub struct MongoPort(pub u16);
pub struct RedisPort(pub u16);


#[macro_export]
macro_rules! config_default_impl {
    // TODO: Implement the macro here
}


// TODO: Use the macro to implement ConfigDefault for each type


// Example usage
pub fn main() {
    // let's say we have a new struct
    struct CustomPort(pub u16);


    // we implement the ConfigDefault trait for CustomPort
    config_default_impl!(CustomPort, 8080);


    // when running the `get_default` method, it should return the default value
    assert_eq!(<CustomPort as ConfigDefault>::get_default().0, 8080);
}