Attribute Macro encoder

#[encoder]

This is an attribute macro that must be used when implementing a Encoder.

It is required to use because a Encoder implementation might introduce new associated types in the future, and this not yet supported on a language level in Rust. So this attribute macro polyfills any missing types automatically.

Note that using derives directly from musli_core requires you to use the #[musli_core::encoder(crate = musli_core)] attribute.

Examples

use std::fmt;

use musli_core::Context;
use musli_core::en::{Encoder, Encode};

struct MyEncoder<'a, C: ?Sized> {
    value: &'a mut Option<u32>,
    cx: &'a C,
}

#[musli_core::encoder(crate = musli_core)]
impl<C: ?Sized + Context> Encoder for MyEncoder<'_, C> {
    type Cx = C;
    type Ok = ();

    fn cx(&self) -> &C {
        self.cx
    }

    fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "32-bit unsigned integers")
    }

    fn encode<T>(self, value: T) -> Result<Self::Ok, C::Error>
    where
        T: Encode<Self::Mode>,
    {
        value.encode(self.cx, self)
    }

    fn encode_u32(self, value: u32) -> Result<(), Self::Error> {
        *self.value = Some(value);
        Ok(())
    }
}