typesafe_builder 0.1.0

A procedural macro for Rust that enables type-safe builder patterns. This crate enforces required, optional, and conditionally required fields at the type level, ensuring safe and flexible struct construction.

Features

• Per-field control: required, optional, and conditionally required (required_if)
• Compile-time enforcement of builder state using type parameters
• Flexible conditional requirements with AND/OR/NOT expressions

Installation

Add the following to your Cargo.toml:

cargo add typesafe_builder

or

[dependencies]
typesafe_builder = "*.*.*"

Usage

Required Field

use typesafe_builder::*;

#[derive(Builder)]
struct User {
    #[builder(required)]
    name: String,
}

let user = UserBuilder::new().with_name("Alice".to_string()).build();

Optional Field

use typesafe_builder::*;

#[derive(Builder)]
struct User {
    #[builder(optional)]
    name: Option<String>,
}

let user = UserBuilder::new().build();
let user2 = UserBuilder::new().with_name("Alice".to_string()).build();

Conditionally Required Field (required_if)

use typesafe_builder::*;

#[derive(Builder)]
struct User {
    #[builder(optional)]
    name: Option<String>,
    #[builder(required_if = "name")]
    age: Option<u8>,
}

// The following will not compile because age is required if name is Some:
let user = UserBuilder::new().with_name("Alice".to_string()).build();

Complex Conditional Expressions

use typesafe_builder::*;

#[derive(Builder)]
struct User {
    #[builder(optional)]
    name: Option<String>,
    #[builder(optional)]
    age: Option<u8>,
    #[builder(optional)]
    address: Option<String>,
    #[builder(required_if = "name && (age || address)")]
    email: Option<String>,
}

// The following will not compile

// because email is required if name and age are Some
let user1 = UserBuilder::new().with_name("Alice".to_string()).with_age(20).build();

// because email is required if name and address are Some
let user2 = UserBuilder::new().with_name("Alice".to_string()).with_address("123 Main St".to_string()).build();

License

MIT