typing-system.md

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Nitro's Typing System

Nitro uses an extensible typing system to efficiently convert between JS and C++ types - statically defined and fully type-safe and null-safe at compile-time.

For example, a JS number will always be a double on the native side:

interface Math extends HybridObject {
  add(a: number, b: number): number
}

class HybridMath : public HybridMathSpec {
  double add(double a, double b);
}

Nitro strictly enforces type-safety and null-safety - both at compile-time and at runtime. This prevents accidentally passing a wrong type to add(..) (for example, a string) and performs null-checks to prevent passing and returning null/undefined values.

On the JS side (TypeScript), type- and null-safety is enforced via TypeScript - so use it!

Nitrogen

Nitrogen ensures that TypeScript definitions are always in sync with native type definitions. You can also use Nitro without nitrogen, in this case TypeScript definitions have to be written manually.

Supported Types

These are all the types Nitro supports out of the box:

JS Type	C++ Type	Swift Type	Kotlin Type
number	double / int / float	Double	Double
boolean	bool	Bool	Boolean
string	std::string	String	String
bigint	int64_t / uint64_t	Int64	Long
T[]	std::vector<T>	[T]	Array<T> / PrimitiveArray
T?	std::optional<T>	T?	T?
[A, B, ...]	std::tuple<A, B, ...>	(A, B) 🟡  (#38)	❌
A | B | ...	std::variant<A, B, ...>	Variant_A_B_C	Variant_A_B_C
(T...) => void	std::function<void (T...)>	@escaping (T...) -> Void	(T...) -> Unit
(T...) => R	std::function<std::shared_ptr<Promise<R>> (T...)>	@escaping (T...) -> Promise<R>	(T...) -> Promise<R>
Sync<(T...) => R>	std::function<R (T...)>	@escaping (T...) -> R	(T...) -> R
Record<string, T>	std::unordered_map<std::string, T>	Dictionary<String, T>	Map<String, T>
Error	std::exception_ptr	Error	Throwable
Promise<T>	std::shared_ptr<Promise<T>>	Promise<T>	Promise<T>
AnyMap	std::shared_ptr<AnyMap>	AnyMap	AnyMap
ArrayBuffer	std::shared_ptr<ArrayBuffer>	ArrayBuffer	ArrayBuffer
Date	std::chrono::system_clock::time_point	Date	java.time.Instant
..any HybridObject	std::shared_ptr<HybridObject>	HybridObject	HybridObject
..any interface	struct T	struct T	data class T
..any enum	enum T	enum T	enum T
..any union	enum T	enum T	enum T