Data Types

Current ASUN schema names are intentionally small and fixed. The only scalar schema names are:

• int
• float
• str
• bool

Scalar Types

ASUN type	Example	Notes
int	42, -100, 0	Any i64-range integer
float	3.14, -0.5, 1e10	Floating-point text form
bool	true, false	Lowercase only
str (unquoted)	Alice Smith	Outer whitespace is trimmed
str (quoted)	" spaces "	Preserves whitespace and supports escapes
null / None	(empty slot)	Empty between commas

Composite Types

Nested Struct

{id@int, address@{city@str, zip@str}}:(
  1,
  (Berlin, 10115)
)

Array / List

{id@int, tags@[str]}:(1, [rust, go, wasm])

Arrays can be nested:

[{matrix@[[int]]}]:
  ([[1, 2], [3, 4]]),
  ([[5, 6], [7, 8]])

Entry List

Keyed collections use an array of entry structs:

{attrs@[{key@str, value@int}]}:([(age, 30), (score, 95)])

Option / Nullable

An empty slot means null / None:

[{id@int, score@float}]:
  (1, 9.5),
  (2,    )

Cross-Language Type Mapping

ASUN type	Rust	Go	Python	Java / Kotlin	Swift	C	C++	Zig	C#	Dart	JS / TS	PHP
int	i64	int64	int	long / Long	Int64	int64_t	int64_t	i64	long	int	number (integer)	int
float	f64	float64	float	double / Double	Double	double	double	f64	double	double	number	float
bool	bool	bool	bool	boolean / Boolean	Bool	bool	bool	bool	bool	bool	boolean	bool
str	String / &str	string	str	String	String	char* / buffer field	std::string	[]const u8	string	String	string	string
null / empty slot	Option<T>	nil / pointer / empty slot	None	nullable field / empty slot	nil / optional	nullable pointer / empty slot	std::optional<T> / empty slot	?T	nullable reference / nullable value	null	null / undefined	null
[T]	Vec<T>	[]T	list	List<T>	[T]	array / repeated rows with schema	std::vector<T>	[]T	List<T> / array	List<T>	T[]	indexed array
nested struct	struct	struct	dict / object factory result	class / data class	AsunValue.object / host model	struct + schema descriptor	struct + metadata macros	struct	class / record implementing schema interface	class implementing AsunSchema	plain object	associative array / object-like array

Notes

• ASUN schema names stay the same in every language: only int, float, bool, str.
• A host language may use a different concrete type name for the same ASUN scalar. For example, Java uses double for float, and Zig commonly maps str to []const u8.
• JS / TS only has one numeric runtime type, so int means “a number that is encoded as an integer”.
• Keyed collections use entry lists such as [{key@str,value@str}].

Language Support Overview

Language	Minimum version	Implementation style	Text decode expects	Binary decode expects
Rust	Rust 1.85+	serde-based generic codec	target type T	target type T
Go	Go 1.24+	reflection + struct tags	output pointer	output pointer
Python	Python 3.8+	compiled C++ extension over Python dict/list values	self-describing text, returns Python objects	explicit schema string
Java / Kotlin	Java 21+, Kotlin helper layer on 1.9+ toolchain	reflection + annotations + class metadata	target Class<T> or Kotlin reified helper	target Class<T> / Kotlin reified helper
Swift	Swift tools 5.9+	native Swift value model around AsunValue	self-describing text, returns AsunValue	self-describing binary, returns AsunValue
C	C11	explicit schema descriptors / macros	schema descriptor + output buffer	schema descriptor + output buffer
C++	C++17	template metadata macros (ASUN_FIELDS, ASUN_TYPES)	target type T	target type T
Zig	Zig 0.15.2+	comptime type introspection	target type T + allocator	target type T + allocator
C#	.NET 8+ (net8.0, net10.0)	IAsunSchema + factory-based typed decode	field bag or factory function	field names + field types + factory
Dart	Dart 3.0+	AsunSchema interface + factory-based typed decode	field bag or factory function	field names + field types + factory
JS / TS	ES2020-capable runtime	runtime object inspection	self-describing text, returns plain objects	explicit schema string
PHP	PHP 8.4+	native C++ extension over arrays / zvals	self-describing text, returns arrays	explicit schema argument

Reading the matrix

• Text ASUN carries its schema in the header, so many dynamic-language implementations can decode it without an external type definition.
• Binary ASUN is intentionally not self-describing. Most implementations therefore need either:
  • a target type,
  • a schema descriptor,
  • or an explicit schema string.
• Swift is the main exception in the current repository: its binary API carries enough typed information to round-trip directly into AsunValue.
• “Implementation style” explains how each language maps host-language data to the common ASUN text and binary formats. The wire format stays the same across languages.

Binary Note

ASUN-BIN may use fixed-width host-language primitives internally, but those widths are not extra schema names.

• The public schema still only uses int, float, bool, and str.
• Binary encoding is little-endian across the official implementations.
• Fixed-width storage details belong to the binary codec implementation, not to the schema surface.