How to Implement the Builder Pattern in Rust

Core
2026-04-17T12:05:42+00:00
Implement the Builder Pattern in Rust using a separate builder struct with setter methods to configure fields before calling build.

Implement the Builder Pattern in Rust by defining a struct with private fields, a separate builder struct with public setter methods, and a build method that constructs the final instance. This approach uses the new method to initialize the builder and chaining setters to configure optional fields before finalizing the object.

struct Email {
    sender: String,
    subject: String,
    content: String,
}

struct EmailBuilder {
    sender: Option<String>,
    subject: Option<String>,
    content: Option<String>,
}

impl EmailBuilder {
    fn new() -> Self {
        EmailBuilder {
            sender: None,
            subject: None,
            content: None,
        }
    }

    fn sender(mut self, sender: String) -> Self {
        self.sender = Some(sender);
        self
    }

    fn subject(mut self, subject: String) -> Self {
        self.subject = Some(subject);
        self
    }

    fn content(mut self, content: String) -> Self {
        self.content = Some(content);
        self
    }

    fn build(self) -> Email {
        Email {
            sender: self.sender.expect("sender is required"),
            subject: self.subject.expect("subject is required"),
            content: self.content.expect("content is required"),
        }
    }
}

fn main() {
    let email = EmailBuilder::new()
        .sender("user@example.com".to_string())
        .subject("Hello".to_string())
        .content("Hi there!".to_string())
        .build();
    println!("Email sent from {}", email.sender);
}