Custom Serialization

Use @serializer(...) and @deserializer(...) when a type needs a custom wire format.

Rules

• Custom serializers and deserializers must always speak valid JSON.
• Custom deserializers should always instantiate and return a new object.
• The optional decorator argument declares the JSON shape used by the custom type.
• If omitted, the shape defaults to any.

Supported shape hints:

• any
• string
• number
• boolean
• object
• array
• nullable forms like string | null

Example

function hexDigit(value: u8): string {
  return String.fromCharCode(value < 10 ? 48 + value : 87 + value);
}

function parseHexNibble(code: u16): u8 {
  if (code >= 48 && code <= 57) return <u8>(code - 48);
  if (code >= 97 && code <= 102) return <u8>(code - 87);
  return <u8>(code - 55);
}

@json
class HexBytes extends Uint8Array {
  constructor(length: i32 = 0) {
    super(length);
  }

  @serializer("string")
  serializer(self: HexBytes): string {
    let out = "";
    for (let i = 0; i < self.length; i++) {
      const value = unchecked(self[i]);
      out += hexDigit(value >> 4);
      out += hexDigit(value & 0x0f);
    }
    return JSON.stringify(out);
  }

  @deserializer("string")
  deserializer(data: string): HexBytes {
    const raw = JSON.parse<string>(data);
    const out = new HexBytes(raw.length >> 1);
    for (let i = 0, j = 0; i < raw.length; i += 2, j++) {
      const hi = parseHexNibble(<u16>raw.charCodeAt(i));
      const lo = parseHexNibble(<u16>raw.charCodeAt(i + 1));
      unchecked((out[j] = <u8>((hi << 4) | lo)));
    }
    return out;
  }
}

Internal helpers

When custom serializers or deserializers call JSON.stringify(...) or JSON.parse(...) internally, the transform rewrites those nested calls to JSON.internal.stringify(...) and JSON.internal.parse(...) so shared buffer state stays scoped correctly.