Crate born

Reuse(Struct, Enum)

It provides functional macros to reuse fields from Struct and Enum definition.

[dependencies]
born = "0.0.1"

Examples

Here, macros to build public struct and enum are used.

If you want to build private struct and enum, just use macros that start with private and shouldn't use pub inside.

Struct

Say you build a demo web server to send private messages.

use born::{
   nested_macro,
   public_struct,
};

public_struct!(
    // pub is required here before struct
    pub struct MessageBase {
        pub text: String
        // pub text: String // , is not required for the struct definition.
    }
);

MessageBase!(
    #[derive(Debug, Clone, PartialEq)]
    pub struct Message {
        pub read: bool,
        // read: bool, // pub is optional.
    }
);

impl Message {
    fn update_text(&mut self, new_message: String) {
        self.text = new_message
    }
    fn read(&mut self) {
        if self.read == false {
           self.read = true;
       }
   }
}

MessageBase!(
   #[derive(Debug, Clone, PartialEq)]
   pub struct MessageCreateRequest
);

MessageBase!(
    // #[derive(Debug, Clone, PartialEq)]
    pub struct MessageUpdateRequest
);

fn main() {
    let message_create_request = MessageCreateRequest {
        text: "I am Steadylearner and 'born' is the crate name.".into(),
    };

    let mut message = Message {
        text: message_create_request.text,
        read: false,
    };
    println!("{:#?}", &message);

    assert_eq!(message, message.clone());

    let message_update_request = MessageUpdateRequest {
        text: "Reuse fields with macros from 'born'.".into(),
    };

    message.update_text(message_update_request.text);
    println!("{:#?}", &message);

    message.read();
    println!("{:#?}", &message);
}

Enum

Compare it with the code example from the Rust documenation.

use born::{
    nested_macro,
    private_enum,
};

private_enum!(
    enum WebEventBase {
        PageLoad,
        PageUnload, // , here is required if you want to extend it.
    }
);

WebEventBase!(
    // #[derive(Debug, Clone, PartialEq)]
    enum WebEvent {
        KeyPress(char),
        Click { x: i64, y: i64 },
        Paste(String),
    }
);

fn inspect(event: WebEvent) {
    match event {
        WebEvent::PageLoad => println!("page loaded"),
        WebEvent::PageUnload => println!("page unloaded"),
        WebEvent::KeyPress(c) => println!("pressed '{}'.", c),
        WebEvent::Paste(s) => println!("pasted \"{}\".", s),
        WebEvent::Click { x, y } => {
            println!("clicked at x={}, y={}.", x, y);
        },
    }
}

fn main() {
    let pressed = WebEvent::KeyPress('x');
    let pasted  = WebEvent::Paste("my text".to_owned());
    let click   = WebEvent::Click { x: 20, y: 80 };
    let load    = WebEvent::PageLoad;
    let unload  = WebEvent::PageUnload;

    inspect(pressed);
    inspect(pasted);
    inspect(click);
    inspect(load);
    inspect(unload);
}

Rename

You can rename struct and enum and reuse the exact same fields.

use born::{
    nested_macro,
    public_struct,
};

public_struct!(
    pub struct UserBase {
        pub first_name: String,
        pub last_name: String,
        pub email: String,
        pub password: String,
    }
);

UserBase!(
    pub struct User {
        pub id: i64,
    }
);

UserBase!(
    pub struct NewUser
);

// It is equal to write these manually.

// pub struct User {
//     pub id: i64,
//     pub first_name: String,
//     pub last_name: String,
//     pub email: String,
//     pub password: String,
// }

// pub struct NewUser {
//     pub first_name: String,
//     pub last_name: String,
//     pub email: String,
//     pub password: String,
// }

Details

• Each struct and enum created from the macros are completely unrelevant to each other except they are built(born) from the same definition

• When you use private_struct! and private_enum!, you can't use pub keyword in it and others use them. It wouldn't be logical if a private struct or private enum can have public fields.

• nested_macro! is required to use the other macros from this crate. It is used to make a macro that creates other macros.

macro_rules! nested_macro {
    ($($body:tt)*) => {
        macro_rules! __nested_macro { $($body)+ }
        __nested_macro!($);
    }
}

Why not attribute macro?

• You can reuse the fields with attribute macro also. But, you need some dependencies.

• If you want more, please read the official documenation about procedural macros.

Macros

nested_macro	You can make a macro that creates other macros with it.
private_enum	Use it to to create, extend and reuse fields from private enum definition.
private_struct	Use it to to create, extend and reuse fields from private struct definition.
public_enum	Similar to private_enum! but public.
public_struct	Similar to private_struct! but public.