omitty

A Rust procedural macro for generating type variants with omitted fields, on-demand.

Features

• On-demand generation - Types created only when used via Omit! macro
• Module-level attribute - Use #[omitty] on modules
• Automatic conversions - impl From<Original> generated automatically
• Type-safe - Compile-time guarantees
• Serde compatible - Works seamlessly with serialization
• Generic support - Preserves type parameters and lifetimes

Installation

[dependencies]
omitty = "0.1.0"
serde = { version = "1.0", features = ["derive"] }

Usage

Basic Example

use omitty::omitty;

#[omitty]
mod api {
    #[derive(omitty::Omittable, Debug, Clone, serde::Serialize, serde::Deserialize)]
    pub struct User {
        pub id: u64,
        pub name: String,
        pub secret_token: String,
    }

    pub struct PublicUser {
        pub user: Omit!(User, secret_token),
    }
}

fn main() {
    let user = api::User {
        id: 42,
        name: "Alice".to_string(),
        secret_token: "super_secret".to_string(),
    };

    let public = api::PublicUser {
        user: user.into(), // automatic From conversion
    };

    let json = serde_json::to_string(&public.user).unwrap();
    // {"id":42,"name":"Alice"}
}

Multiple Omitted Fields

#[omitty]
mod api {
    #[derive(omitty::Omittable, Debug, Clone, serde::Serialize, serde::Deserialize)]
    pub struct User {
        pub id: u64,
        pub name: String,
        pub email: String,
        pub password_hash: String,
        pub secret_token: String,
    }

    pub struct PublicProfile {
        pub user: Omit!(User, password_hash, secret_token, email),
    }

    pub struct AdminView {
        pub user: Omit!(User, secret_token),
    }
}

Generic Types

#[omitty]
mod api {
    #[derive(omitty::Omittable, Debug, Clone)]
    pub struct User<T> {
        pub id: u64,
        pub name: String,
        pub secret: String,
        pub metadata: T,
    }

    pub struct PublicUser<T> {
        pub user: Omit!(User<T>, secret),
    }
}

How It Works

1. Mark your module with #[omitty]
2. Derive Omittable on your struct
3. Use Omit!(Type, field1, field2, ...) in field types
4. Types are generated automatically as __omitty__Type::TypeWithout_field1_field2
5. impl From<Type> is generated for easy conversion

Generated Code

For Omit!(User, secret_token), omitty generates:

pub mod __omitty__User {
    pub struct UserWithout_secret_token {
        pub id: u64,
        pub name: String,
    }

    impl From<super::User> for UserWithout_secret_token {
        fn from(value: super::User) -> Self {
            Self { id: value.id, name: value.name }
        }
    }
}

Benefits

• Zero boilerplate - No manual type definitions
• DRY principle - Single source of truth
• Type safety - Compile-time checks
• Performance - Zero runtime overhead
• Flexibility - Mix and match omitted fields

License

MIT OR Apache-2.0