/impl-new-derive

A macro that generates a constructor for Rust structs, initializing public fields from arguments and private fields with default values, supporting generic and non-generic types.

Primary LanguageRust

impl-new-derive

The impl-new-derive procedural macro generates a new constructor for Rust structs. This macro automatically creates a constructor that initializes public fields from provided arguments and initializes private fields with default values using the Default::default() method.

Features

  • Automatically generates a constructor (new) for structs.
  • Handles public fields: The new function takes all public fields of the struct as arguments.
  • Handles private fields: All non-public fields are automatically initialized with their Default::default() values.
  • Supports generic types: The macro works with both generic and non-generic structs.

Usage

  1. Add the macro to your project by including the crate that defines the procedural macro in your Cargo.toml:
[dependencies]
impl_new_derive = "0.1.0"
  1. Annotate your struct with #[derive(ImplNew)] to automatically generate a new constructor.

Example for a Non-Generic Struct

use impl_new_derive::ImplNew;

#[derive(ImplNew, Default)]
struct MyStruct {
    pub name: String,
    pub age: u32,
    secret: String, // This field is private
}

fn main() {
    let my_struct = MyStruct::new("John".to_string(), 30);
    println!("Name: {}, Age: {}", my_struct.name, my_struct.age);
}

In this example:

  • The new function takes name and age as arguments, because they are public fields.
  • The secret field is initialized to Default::default() since it's private and not included in the function arguments.

Example for a Generic Struct

use impl_new_derive::ImplNew;

#[derive(ImplNew, Default)]
struct MyStruct<T> {
    pub value: T,
    count: usize, // This field is private
}

fn main() {
    let my_struct = MyStruct::new(42);
    println!("Value: {}", my_struct.value);
}

In this generic struct example:

  • The new function takes value as an argument.
  • The count field, being private, is automatically initialized with Default::default().

How It Works

When you annotate a struct with #[derive(ImplNew)], the macro performs the following actions:

  • It iterates over the fields of the struct.
  • For public fields, it adds them as arguments to the generated new function.
  • For non-public fields, it automatically initializes them with Default::default().
  • If the struct contains generics, the macro correctly handles them in the impl block.

Limitations

  • The macro only works with structs that have named fields (i.e., struct with named members).
  • If the struct contains fields that do not implement Default, the macro will fail to compile.

Contributing

Feel free to open issues or pull requests if you have any suggestions or improvements.

License

This project is licensed under the MIT License.