Crate structural_typing 

Structural Typing for Rust

Define a struct once and use it with different field combinations, tracked at compile time.

Installation

cargo add structural-typing

If using derives on #[structural] structs, also add:

cargo add derive-where

Quick Example

use structural_typing::{structural, presence::Present, select};

#[structural]
struct User { id: u32, name: String, email: String }

type Create = select!(user: name, email);

fn create_user(data: User<Create>) -> User {
    data.id(generate_id())
}

fn update_user<F: user::Fields<id = Present>>(data: User<F>) {
    if let Some(name) = data.get_name() {
        update_in_db(data.id, name);
    }
}

Core Concepts

• Field States: Present, Optional, Absent
• Builder API: .field(value) infers presence from type
• Type Selection: select! macro or type aliases
• Bounded Impls: Require specific fields via trait bounds
• Merge and Extract: Combine partial structs or extract field subsets

For serde integration and other details, see the structural macro documentation.

See the examples directory for comprehensive usage.

Constraints

• Named structs only (not tuple structs or enums)
• No generic parameters
• At least one field required

Modules

access

Runtime field access trait for checking presence and getting values. Runtime field access for structural types.

extract

Traits for splitting structs into selected fields and remainder. Extract selected fields from structs, returning the selected fields and remainder.

presence

Type-level presence markers and traits for field state tracking. Type-level markers for field presence states.

Macros

select

Construct a FieldSet by selecting fields from a module.

Attribute Macros

structural

Generates type-safe structural typing support for a struct.