Custom filter to use Display implementation generically?

[ZakSingh]

I have some structs that require special formatting. I'd like to use their Display implementation. Right now I have a filter for each struct:

pub fn currency_filter(val: ViaDeserialize<Currency>) -> String {
    format!("{}", (val.0))
}

pub fn assembly_status_filter(val: ViaDeserialize<PhoneNumber>) -> String {
    format!("{}", val.0)
}

etc...

Is there a way to write a generic filter that takes any struct that can be deserialized and has a display implementation?

[mitsuhiko]

Not like this. If you work with objects via ViaDeserialize minijinja will need the type information carried side by side like this. However if your objects like PhoneNumber, Currency etc. were to implement Object then you could pass it as Value::from_object(...) to the context and pass it as Value to the filter:

use std::fmt;
use std::sync::Arc;

use minijinja::value::{Object, ObjectRepr};
use minijinja::{context, Environment, Value};

#[derive(Debug)]
struct PhoneNumber {
    digits: Vec<u8>,
}

impl Object for PhoneNumber {
    fn repr(self: &Arc<Self>) -> ObjectRepr {
        ObjectRepr::Plain
    }

    fn render(self: &Arc<Self>, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "+")?;
        for digit in &self.digits {
            write!(f, "{}", digit)?;
        }
        Ok(())
    }
}

fn main() {
    let mut env = Environment::new();

    env.add_template("hello.txt", "Call me at {{ number }}!")
        .unwrap();
    let template = env.get_template("hello.txt").unwrap();
    let number = Value::from_object(PhoneNumber {
        digits: vec![2, 3, 5, 2, 1, 5],
    });
    println!("{}", template.render(context!(number)).unwrap());
}

Objects are quite powerful and they are highly dynamic, so you have more flexibility.

[ZakSingh]

That's exactly what I was looking for! I wasn't aware of the Object trait. Thank you!