Understanding Rust's Trait System:

One feature in Rust which types can use is these are called traits. Attributes designate the activities that every type can have in common.

Example of a Trait:

                    
pub trait Summarizable {
    fn summary(&self) -> String;
}
                    
                  

• Defining a Trait: Use the trait keyword followed by the trait name. Inside the trait, define method signatures that implementors of the trait must provide.

Implementing Traits for Custom Types

To implement a trait for a custom type, use the impl keyword followed by the trait name for the type.

Example:

                    
pub trait Summarizable {
    fn summary(&self) -> String;
}

pub struct Article {
    pub title: String,
    pub author: String,
    pub content: String,
}

impl Summarizable for Article {
    fn summary(&self) -> String {
        format!("{} by {}", self.title, self.author)
    }
}

fn main() {
    let article = Article {
        title: String::from("Rust Programming"),
        author: String::from("John Doe"),
        content: String::from("Rust is a systems programming language..."),
    };

    println!("Article Summary: {}", article.summary());
}
                    
                  

• Implementing a Trait: Use impl TraitName for TypeName and provide implementations for the trait's methods.
• Using Trait Methods: Once a type implements a trait, you can call the trait's methods on instances of that type.

Default Method Implementations:

Traits can also give some methods with their default implementations so that those will be overridden by implementors.

Example:

                    
pub trait Summarizable {
    fn summary(&self) -> String {
        String::from("(Read more...)")
    }
}

pub struct Article {
    pub title: String,
    pub author: String,
    pub content: String,
}

impl Summarizable for Article {
    fn summary(&self) -> String {
        format!("{} by {}", self.title, self.author)
    }
}

pub struct Tweet {
    pub username: String,
    pub content: String,
}

impl Summarizable for Tweet {}

fn main() {
    let article = Article {
        title: String::from("Rust Programming"),
        author: String::from("John Doe"),
        content: String::from("Rust is a systems programming language..."),
    };

    let tweet = Tweet {
        username: String::from("@rustacean"),
        content: String::from("Learning Rust is fun!"),
    };

    println!("Article Summary: {}", article.summary());
    println!("Tweet Summary: {}", tweet.summary());
}
                    
                  

• Default Methods: Put default abstruction in the trait definition. Implementors can rewrite these methods or use the default ones.

Deriving Traits Automatically

Rust can automatically generate implementations for certain traits using the derive attribute.

Commonly derived traits include Clone, Copy, Debug, PartialEq, and Eq.

Example:

                    
#[derive(Debug, Clone, PartialEq)]
pub struct Point {
    pub x: i32,
    pub y: i32,
}

fn main() {
    let point1 = Point { x: 5, y: 10 };
    let point2 = point1.clone();

    println!("{:?}", point1); // Debug
    println!("{}", point1 == point2); // PartialEq
}
                    
                  

• Deriving Traits: Use #[derive(Trait1, Trait2, ...)] above the struct or enum definition.
• Common Traits:
• Debug: Formats the value using the {:?} formatter.
• Clone: Creates a deep copy of the value.
• PartialEq: Allows comparison using == and !=.

Custom Derive Macros:

Besides, you can define derive macros of your own implementation to achieve this. This is an advanced functional and it often deals with procedural macros.

Summary

• Traits: Define shared behavior across types using the trait keyword.
• Implementing Traits: Use impl TraitName for TypeName to implement traits for custom types.
• Default Implementations: Traits can also have default method implementations, which can be overridden in particular implementations of the trait.
• Deriving Traits: Use the #[derive(Trait)] attribute to automatically generate implementations for common traits like Debug, Clone, and PartialEq.

The Rust trait system provides a strong tool which allows developers to declare and share behavior among different types, thus polymorphism and code reuse. Through the process of combining manual implementations with automatic derivations, you can compose fast, as well as reliable Rust code.