data NativeDecoder

use std.ser { Codec, Encoder, Decoder, Schema, encode, decode, hex, EncodeError, DecodeError }

data Shift {}

impl Codec<i64> for Shift {
  static fn encode(x: &i64, w: &var Encoder) -> () | EncodeError { w.writeI64(x + 1) }
  static fn decode(r: &var Decoder) -> i64 | DecodeError { r.readI64()? - 1 }
  static fn schema() -> Schema => Schema.of("int64")
}

data Subject {
  @codec(Shift) n: i64
}

fn main() io {
  let b = encode(&Subject{ n: 9 })!
  print("{decode<Subject>(&b)!.n}")
}

9