Codegen Typings

TypeScript types supported by RNUE Codegen and their generated Unreal C++ types.

@rnue/codegen converts TypeScript types to Unreal C++ types according to the convention below.

Typings map

TypeScript	Nullable or optional TypeScript	Generated Unreal C++	Nullable or optional Unreal C++
`string`	`string \| null` or `value?: string`	`FString`	`TOptional<FString>`
`boolean`	`boolean \| null` or `value?: boolean`	`bool`	`TOptional<bool>`
`number`	`number \| null` or `value?: number`	`double`	`TOptional<double>`
`CodegenTypes.Double`	`CodegenTypes.Double \| null`	`double`	`TOptional<double>`
`CodegenTypes.Float`	`CodegenTypes.Float \| null`	`double`	`TOptional<double>`
`CodegenTypes.Int32`	`CodegenTypes.Int32 \| null` or `value?: CodegenTypes.Int32`	`int32`	`TOptional<int32>`
`ReadonlyArray<T>` or `Array<T>`	`ReadonlyArray<T> \| null` or `value?: ReadonlyArray<T>`	`TArray<T>`	`TOptional<TArray<T>>`
Object alias or inline object	Nullable or optional object	Generated `F` struct	`TOptional<FRecord>`
`Partial<RecordType>`	—	Generated `F` struct with optional fields	Each optional field uses `TOptional<T>`
String-literal union, such as `"slow" \| "fast"`	Nullable or optional union	Generated scoped `E` enum	`TOptional<EMode>`
`void` return	—	`void`	—

CodegenTypes.Int32 uses strict conversion. The generated binding rejects fractional, non-finite, and out-of-range values.
Object aliases generate structs in the <Library>::Generated namespace. Field names use PascalCase, and Boolean fields use the b prefix.
Nested concrete records are supported. Recursive records are not supported.
For an applicable schema type, null or undefined produces an unset TOptional<T>.
An optional-only parameter accepts omission or undefined. Add null to its TypeScript type when the caller can pass null.

Use runtime jsi values only when the schema cannot describe a concrete value.

TypeScript	Nullable or optional TypeScript	Generated C++	Notes
`CodegenTypes.UnsafeObject` or dictionary type	Nullable or optional object	`facebook::jsi::Object` or `TOptional<facebook::jsi::Object>`	Untyped JavaScript object
`CodegenTypes.UnsafeMixed` or `unknown`	Nullable or optional value	`facebook::jsi::Value` or `TOptional<facebook::jsi::Value>`	Dynamic JavaScript value
Function or callback	Nullable or optional function	`facebook::jsi::Function` or `TOptional<facebook::jsi::Function>`	Runtime-bound callback
Array that contains a runtime-bound type	Nullable or optional array	`facebook::jsi::Array` or `TOptional<facebook::jsi::Array>`	The complete array remains runtime-bound
Non-string union	Nullable or optional union	`facebook::jsi::Value` or `TOptional<facebook::jsi::Value>`	Dynamic union value
TypeScript `enum`	Nullable or optional enum	`facebook::jsi::Value` or `TOptional<facebook::jsi::Value>`	Use a string-literal union for a generated C++ enum
Direct tuple	—	Not generated	React Native 0.86 erases tuple element types
Array of tuples	Nullable or optional array	`facebook::jsi::Array` or `TOptional<facebook::jsi::Array>`	Tuple element types are not available to RNUE Codegen

A method that contains a runtime-bound type receives facebook::jsi::Runtime& Runtime.
A fully concrete method does not receive a JSI runtime.
Raw JSI values belong to that runtime and its JavaScript thread. Do not store them or move them to another thread.
Copy the required data to Unreal-owned values before asynchronous work starts.
Concrete records and event payloads cannot contain runtime-bound fields. Keep each dynamic value at a method boundary.
Dictionary types do not generate TMap. Callback signatures do not generate typed C++ callback wrappers.
any is not a supported schema type. Use CodegenTypes.UnsafeMixed when the boundary must accept dynamic data.

@rnue/codegen changes TypeScript declarations into generated IService methods and protected event helpers.

TypeScript declaration	Generated C++ service shape
`setEnabled(enabled: boolean): void`	`void SetEnabled(bool bEnabled)`
`getName(): string`	`FString GetName()`
`getName(): string \| null`	`TOptional<FString> GetName()`
`load(): Promise<Result>`	`void Load(ReactNativeUnreal::TReactPromise<FResult> Promise)`
`load(): Promise<Result \| null>`	`void Load(ReactNativeUnreal::TReactPromise<TOptional<FResult>> Promise)`
`clear(): Promise<void>`	`void Clear(ReactNativeUnreal::TReactPromise<void> Promise)`
`readonly onReading: CodegenTypes.EventEmitter<Reading>`	Protected `bool EmitReading(FReading Value)`

Typed Promise handles are thread-safe and settle once. They become inert when their React endpoint disconnects.
Use Promise.Resolve(Value) or Promise.Resolve() for success. Use Promise.Reject(ReactNativeUnreal::FReactModuleError(...)) for an error.
A Promise with a runtime-bound result remains a raw JSI Promise. The service returns facebook::jsi::Value.
The same method receives facebook::jsi::Runtime& Runtime and const std::shared_ptr<facebook::react::CallInvoker>& JsInvoker.
Event emitters and their payloads are not nullable. Event payloads must use concrete types.
JavaScript receives an EventSubscription and must call remove() during cleanup.

@rnue/codegen uses the following C++ naming rules: