Deprecation Notice: This crate is deprecated in favor of the derive_new crate. Please use the derive_new crate instead of this crate.

Impl New 🦀

A procedural macro to generate a new function implementation for your struct.

🚀 Add to your project

Add this to your Cargo.toml:

[dependencies]
impl_new = "0.2.0"

Or run this command in your workspace:

cargo add impl_new

❓ What is the new function?

The new function is a function that is used to create a new instance of a struct. It is a common pattern in Rust to use a new function to create a new instance of a struct instead of using the struct directly. This is because it is easier to add new fields to the struct without breaking the code that uses it.

👨‍💻 Usage

Is simple, just derive the impl_new::New proc macro on your struct and it will generate a new function for you.

For Named Fields

#[derive(impl_new::New)]
struct Foo {
    name: String,
    age: usize,
}

// The generated code will look like this:
// impl Foo {
//     pub fn new(name: impl Into<String>, age: Into<usize>) -> Self {
//         Self { name: name.into(), age: age.into() }
//     }
// }

fn main() {
    let foo = Foo::new("Hello", 42usize); // Will use `Into::into` to convert the arguments to the fields types.
    assert_eq!(foo.name, "Hello".to_string());
    assert_eq!(foo.age, 42);
}

For Unnamed Fields

Note: The #[impl_new(name = "name")] attribute is required for unnamed fields.

#[derive(impl_new::New)]
struct Foo(#[impl_new(name = "name")] String, #[impl_new(name = "age")] usize);

// The generated code will look like this:
// impl Foo {
//     pub fn new(name: impl Into<String>, age: Into<usize>) -> Self {
//         Self(name.into(), age.into())
//     }
// }

fn main() {
    let foo = Foo::new("Hello", 42usize); // Will use `Into::into` to convert the arguments to the fields types.
    assert_eq!(foo.0, "Hello".to_string());
    assert_eq!(foo.1, 42);
}

🛹 Attributes

#[impl_new(name = "name")]

The name option specifies the name of the argument in the new function.

Note: This attribute is required for unnamed fields.

Example

#[derive(impl_new::New)]
struct User(#[impl_new(name = "username")] String, #[impl_new(name = "age")] i32);

// The generated code will look like this:
// impl User {
//     pub fn new(username: impl Into<String>, age: Into<i32>) -> Self {
//         Self(username.into(), age.into())
//     }

fn main() {
    let user = User::new("Hello", 42); // Will use `Into::into` to convert the arguments to the fields types.
    assert_eq!(user.0, "Hello".to_string());
    assert_eq!(user.1, 42);
}

#[derive(impl_new::New)]
struct User {
    #[impl_new(name = "username")]
    name: String,
    #[impl_new(name = "user_age")]
    age: i32,
}

// The generated code will look like this:
// impl User {
//     pub fn new(username: impl Into<String>, user_age: Into<i32>) -> Self {
//         Self { name: username.into(), age: user_age.into() }
//     }
// }

fn main() {
    let user = User::new("Hello", 42); // Will use `Into::into` to convert the arguments to the fields types.
    assert_eq!(user.name, "Hello".to_string());
    assert_eq!(user.age, 42);
}

#[impl_new(default)]

The default option will remove the field from the new function arguments and use the default value of the field type instead.

Note: This option is conflict with the name option, because the field will be removed from the new function arguments.

Example

#[derive(impl_new::New, Default, Debug, PartialEq)]
struct User {
    name: String,
    #[impl_new(default)]
    is_admin: bool,
}

// The generated code will look like this:
// impl User {
//     pub fn new(name: impl Into<String>) -> Self {
//         Self { name: name.into(), is_admin: bool::default() }
//     }
// }

#[derive(impl_new::New)]
struct Foo(#[impl_new(name = "somthing")] String, #[impl_new(default)] User);

// The generated code will look like this:
// impl Foo {
//     pub fn new(somthing: impl Into<String>) -> Self {
//         Self(somthing.into(), User::default())
//     }
// }

fn main() {
    let user = User::new("Hello"); // Will use `Into::into` to convert the arguments to the fields types.
    let some_foo = Foo::new("Hello"); // Will use `Into::into` to convert the arguments to the fields types.
    assert_eq!(user.name, "Hello".to_string());
    assert_eq!(user.is_admin, false);
    assert_eq!(some_foo.0, "Hello".to_string());
    assert_eq!(some_foo.1, User::default());
}

#[impl_new(value = || <VALUE>)]

The value option will set the field value to the given value.

Note: This option is conflict with the name and default options, because the field will be removed from the new function arguments.

Note: The value must be a closure that returns the field type.

Example

#[derive(impl_new::New)]
struct User {
    name: String,
    #[impl_new(value = || true)]
    is_active: bool,
}

// The generated code will look like this: (Not exactly, but you get the idea)
// impl User {
//     pub fn new(name: impl Into<String>) -> Self {
//         Self { name: name.into(), is_active: true }
//     }
// }

#[derive(impl_new::New)]
struct Foo(#[impl_new(name = "name")] String, #[impl_new(value = || true)] bool);

// The generated code will look like this: (Not exactly, but you get the idea)
// impl Foo {
//     pub fn new(name: impl Into<String>) -> Self {
//         Self(name.into(), true)
//     }
// }

fn main() {
    let user = User::new("Bob"); // Will use `Into::into` to convert the arguments to the fields types.
    let some_foo = Foo::new("Bob"); // Will use `Into::into` to convert the arguments to the fields types.
    assert_eq!(user.name, "Bob".to_string());
    assert_eq!(user.is_active, true);
    assert_eq!(some_foo.0, "Bob".to_string());
    assert_eq!(some_foo.1, true);
}

🤗 Contributing

Contributions are welcome! You can contribute in many ways, for example:

• Improve the documentation.
• Add more tests.
• Add more examples.
• Report a bug by opening an issue.
• Suggest a new feature by opening an issue.
• Fix a bug or add a new feature. (Please open an issue first if you want to add a new feature or if you want to fix a bug that doesn't have an issue yet.)
• Fix a typo.
• Refactor the code.
• Improve the error messages.

🤝 Code of Conduct

We are committed to providing a friendly, safe and welcoming environment for all. Please read and respect the Code of Conduct.

📝 Changelog

See CHANGELOG.md.

🔑 License

This project is licensed under the MIT license.