CustomDefault

Derive macro for Default trait with customization

lib.rs:

CustomDefault

Provides derive macro for Default trait with customization point

Attributes

• def_val=<value> - Specifies default value for field. Panics on incorrect type of field.
• def_exp="expression" - Specifies expression to be placed as initializer to field. No pre-processing.

Usage

use cute_custom_default::CustomDefault;

pub fn default_value_string() -> &'static str {
    "default_value_string"
}

#[derive(CustomDefault)]
pub struct MyStruct {
    #[def_val='c']
    pub custom_char: char,
    #[def_val=b"my_bytes"]
    pub custom_bytes: [u8; 8],
    #[def_val=b"my_bytes"]
    pub custom_bytes_slice: &'static [u8],
    #[def_val=b'b']
    pub custom_default: u8,
    #[def_val=true]
    pub custom_bool: bool,
    pub normal_bool: bool,
    #[def_exp="\"Just my string\".to_owned()"]
    pub expression: String,
    #[def_exp="default_value_string()"]
    pub static_str: &'static str,
    #[def_val="Just my string"]
    pub string: String,
    #[def_val="Just my string"]
    pub static_str_again: &'static str,
    #[def_val=666]
    pub u32_field: u32,
    #[def_exp="std::u16::MAX"]
    pub u16_field: u16,
    #[def_exp="-655_555"]
    pub i32_field: i32,
}

fn main() {
    let my_struct = MyStruct::default();
    assert_eq!(my_struct.custom_char, 'c');
    assert_eq!(my_struct.custom_default, b'b');
    assert_eq!(&my_struct.custom_bytes, b"my_bytes");
    assert_eq!(my_struct.custom_bytes_slice, b"my_bytes");
    assert_eq!(my_struct.custom_bool, true);
    assert_eq!(my_struct.normal_bool, false);
    assert_eq!(my_struct.expression, "Just my string");
    assert_eq!(my_struct.static_str, default_value_string());
    assert_eq!(my_struct.string, "Just my string");
    assert_eq!(my_struct.static_str_again, "Just my string");
    assert_eq!(my_struct.u32_field, 666);
    assert_eq!(my_struct.u16_field, std::u16::MAX);
    assert_eq!(my_struct.i32_field, -655_555);
}