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//! This example shows combining generics with custom errors and validation.
//!
//! Note the use of the type parameter in the `#[builder(...)]` attribute.
#![allow(dead_code)]
#[macro_use]
extern crate derive_builder;
use derive_builder::UninitializedFieldError;
trait Popular {
fn is_popular(&self) -> bool;
}
impl<'a> Popular for &'a str {
fn is_popular(&self) -> bool {
!self.starts_with('b')
}
}
#[derive(Debug, Builder)]
#[builder(build_fn(validate = "check_person", error = "Error<N>"))]
struct Person<N: Popular + Clone> {
name: N,
age: u16,
}
#[derive(Debug)]
enum Error<N> {
UninitializedField(&'static str),
UnpopularName(N),
}
impl<N> From<UninitializedFieldError> for Error<N> {
fn from(error: UninitializedFieldError) -> Self {
Self::UninitializedField(error.field_name())
}
}
fn check_person<N: Popular + Clone>(builder: &PersonBuilder<N>) -> Result<(), Error<N>> {
if let Some(name) = &builder.name {
if !name.is_popular() {
return Err(Error::UnpopularName(name.clone()));
}
}
Ok(())
}
fn main() {
dbg!(PersonBuilder::default()
.name("bill")
.age(71)
.build()
.unwrap_err());
}
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