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//! This example illustrates the use of `validate` to add a pre-build validation
//! step.
use derive_builder::Builder;
#[derive(Builder, Debug, PartialEq)]
#[builder(build_fn(validate = Self::validate))]
struct Lorem {
pub ipsum: u8,
}
impl LoremBuilder {
/// Check that `Lorem` is putting in the right amount of effort.
fn validate(&self) -> Result<(), String> {
if let Some(ref ipsum) = self.ipsum {
match *ipsum {
i if i < 20 => Err("Try harder".to_string()),
i if i > 100 => Err("You'll tire yourself out".to_string()),
_ => Ok(()),
}
} else {
Ok(())
}
}
}
fn main() {
// If we're trying too hard...
let x = LoremBuilder::default().ipsum(120).build().unwrap_err();
// .. the build will fail:
assert_eq!(&x.to_string(), "You'll tire yourself out");
}
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