EzInit

Initialize structs easily with powerful derive macros.

How does it work?

If you derive EzInit on your struct, it will generate a new() function that initializes the struct fields based on the following rules:

Field Initialization Modes

1. Explicit Default Value: #[init(default = <expression>)]

   • Uses the provided expression to initialize the field
   • Example: #[init(default = 100)], #[init(default = "hello".to_string())]

2. Default Trait: #[init(default)]

   • Uses Default::default() for types that implement Default
   • Example: #[init(default)] on a field of type CharacterClass (if it derives Default)

3. Random Values: #[init(random)] or #[init(random = "range")] or #[init(random = [items])]

   • #[init(random)]: Random value using the type's standard random generation
   • #[init(random = "1..10")]: Random integer in range
   • #[init(random = "0.0..1.0")]: Random float in range
   • #[init(random = ["A", "B", "C"])]: Random item from list

4. Random Enum Variant: #[init(enum)]

   • Picks a random variant from an enum that derives RandomVariant
   • The enum must only have unit variants (no data)

5. Option Types: No attribute needed

   • Automatically initialized to None

6. Required Fields: No attribute

   • Becomes a required parameter in the new() function

RandomVariant Derive

For enums, derive RandomVariant to enable random variant selection:

• Only works on enums with unit variants (no associated data)
• Can be combined with Default derive for flexible initialization
• Implements Distribution<YourEnum> for rand::distributions::Standard

Installation

Not published yet, so you need to clone the repo and add it as a path dependency:

[dependencies]
ezinit = { path = "path/to/ezinit" }

Usage Example

use ezinit::{EzInit, RandomVariant};

// Derive RandomVariant for random enum selection
#[derive(Debug, Clone, Copy, Default, RandomVariant)]
enum RoadCondition {
    #[default]
    Excellent,
    Good,
    Fair,
    Poor,
    Fatal,
}

#[derive(Debug, Clone, Copy, Default)]
enum RoadType {
    Highway,
    #[default]
    Street,
    Avenue,
    Hill
}

// Derive EzInit to generate the new() function
#[derive(Debug, EzInit)]
struct HighWay {
    // Required field: must be passed to new()
    pub name: String,

    // Explicit default value
    #[init(default = 2)]
    pub lanes: u32,

    // Random item from list
    #[init(random = ["Me", "Cat", "Politician"])]
    pub built_by: String,

    // Use Default::default() - always returns street
    #[init(default)]
    pub road_type: RoadType,

    // Random enum variant
    #[init(enum)]
    pub condition: RoadCondition,

    // Random integer range
    #[init(random = "60..120")]
    pub max_speed: u32,

    // Random float range
    #[init(random = "0.0..100.0")]
    pub length_km: f64,

    // Option: automatically None
    pub toll_cost: Option<f32>,
}

fn main() {
    // Only 'name' is required!
    let highway = HighWay::new("I-95".to_string());
    
    println!("Highway: {}", highway.name);
    println!("Type: {:?} (always default), Condition: {:?} (random)", 
             highway.road_type, highway.condition);
    println!("Built by: {}, Lanes: {}", highway.built_by, highway.lanes);
    println!("Max Speed: {} km/h, Length: {:.1} km", 
             highway.max_speed, highway.length_km);
}

Sample Output

Running the above code produces output like this (values marked as random will differ each run):

Highway: I-95
Type: Street (always default), Condition: Good (random)
Built by: Cat, Lanes: 2
Max Speed: 87 km/h, Length: 42.7 km

Each time you run the program, the random values will change:

Highway: I-95
Type: Street (always default), Condition: Fatal (random)
Built by: Politician, Lanes: 2
Max Speed: 103 km/h, Length: 15.3 km

Generated Code

For the above example, EzInit generates:

impl HighWay {
    pub fn new(name: String) -> Self {
        Self {
            name,
            lanes: 2,
            built_by: {
                use ::ezinit::export::rand::seq::SliceRandom;
                ["Me", "Cat", "Politician"]
                    .choose(&mut ::ezinit::export::rand::thread_rng())
                    .unwrap()
                    .clone()
                    .into()
            },
            road_type: Default::default(),
            condition: ::ezinit::export::rand::random(),
            max_speed: ::ezinit::export::rand::Rng::gen_range(
                &mut ::ezinit::export::rand::thread_rng(),
                60..120
            ),
            length_km: ::ezinit::export::rand::Rng::gen_range(
                &mut ::ezinit::export::rand::thread_rng(), 
                0.0..100.0
            ),
            toll_cost: None,
        }
    }
}

License

MIT