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Learn Rust Coding · Lesson

The Builder Pattern

Construct objects step by step.

Why a Builder?

Rust has no named or optional function arguments. When a struct has many fields, especially optional ones, a constructor with eight positional parameters becomes unreadable and error-prone.

The builder pattern solves this. You configure an object step by step with named methods, then call a final build() to produce the value. It reads like a fluent sentence.

The Target Struct

Start with the type you actually want to construct. Here a server configuration carries a required host plus several optional knobs.

Notice the fields are private to encourage construction through the builder rather than struct literals.

pub struct ServerConfig {
    host: String,
    port: u16,
    max_connections: usize,
    use_tls: bool,
}

All lessons in this course

  1. The Builder Pattern
  2. The Newtype Pattern
  3. Type-State Builders
  4. Deref and Wrapper Ergonomics
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