builder-pattern 0.4.2

A derivable macro for declaring a builder pattern.
Documentation 
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use builder_pattern::Builder;
use core::cmp::Ordering;

#[derive(Builder, Debug, PartialEq)]
struct Test {
    #[validator(to_positive)]
    positive: i32,
}

fn to_positive(val: i32) -> Result<i32, &'static str> {
    match val.cmp(&0) {
        Ordering::Greater => Ok(val),
        Ordering::Less => Ok(-val),
        Ordering::Equal => Err("The input value is zero."),
    }
}

fn main() {
    let a = Test::new().positive(5).unwrap().build();
    let b = Test::new().positive(-5).unwrap().build();
    println!("a: {:?}, b: {:?}", a, b);
    assert_eq!(a, Test { positive: 5 });
    assert_eq!(b, Test { positive: 5 });

    let c = Test::new().positive(0);
    assert!(c.is_err());
    if let Err(err) = c {
        println!("{}", err);
    }
}