Supported Types

This page lists the Dart types you can use in Fory messages, and flags where you need to be careful for cross-language compatibility.

Built-in Primitive Types

The following Dart types serialize directly without any special handling:

Dart type	Cross-language notes
bool	Direct mapping
int	Serialized as 64-bit by default. Use wrappers or @Int32Type etc. when the peer expects a narrower integer
double	Maps to 64-bit float. Use Float32 wrapper when the peer expects 32-bit
String	Direct mapping
Uint8List	Binary blob
List, Set, Map	Supported; element types must also be supported
DateTime	Use Timestamp or LocalDate wrappers for explicit semantics

Integer Wrappers

Dart int is 64-bit at runtime. If the peer language expects a 32-bit integer (Java int, Go int32, C# int) and you send a Dart int, the deserialization may fail or silently truncate.

Use an integer wrapper class to pin the exact wire width:

final Int8 tiny = Int8(-1);        // 8-bit signed
final Int16 shortValue = Int16(7); // 16-bit signed
final Int32 age = Int32(36);       // 32-bit signed — matches Java int, C# int, Go int32
final UInt8 flags = UInt8(255);    // 8-bit unsigned
final UInt16 port = UInt16(65535); // 16-bit unsigned
final UInt32 count = UInt32(4000000000); // 32-bit unsigned

Each wrapper clamps the stored value to the target bit width.

Floating-Point Wrappers

Dart double maps to 64-bit float. If the peer uses a 32-bit float, use a wrapper:

• Float32 — 32-bit float (matches Java float, C# float, Go float32)
• Float16 — half-precision, for specialized numeric payloads

Time and Date Types

Avoid sending raw DateTime across languages — time zone handling and epoch differences vary. Use the explicit wrappers instead:

• Timestamp — a UTC instant with nanosecond precision (seconds + nanoseconds)
• LocalDate — a calendar date without time or time zone

final now = Timestamp.fromDateTime(DateTime.now().toUtc());
final birthday = LocalDate(1990, 12, 1);

Structs and Enums

Annotate classes with @ForyStruct() and run build_runner to make them serializable. Enums in the same file are included automatically.

@ForyStruct()
class User {
  User();

  String name = '';
  Int32 age = Int32(0); // use Int32 when peers expect a 32-bit integer
}

See Code Generation.

Collections

Fory supports List<T>, Set<T>, and Map<K, V>. Element and key types must also be serializable types. Avoid using mutable objects as map keys.

Compatibility Tip

When in doubt about whether a Dart type will match what the peer expects, use the explicit wrapper types. Guessing the wrong numeric width is one of the most common cross-language bugs.

Related Topics

• Field Configuration
• Cross-Language
• Schema Evolution