Macros

swift4j provides three macros, all in the Swift4j module.

@jvm

Marks a Swift class, struct, or enum for export to Java and Kotlin.

@jvm
class MyService { ... }

@jvm
struct Config { ... }

@jvm
enum Status { case active, inactive }

When applied, the macro:

• Adds JNI registration code that runs when the native library is loaded
• Generates native C entry points for each exported member
• Adds conformance to the internal JObjectConvertible protocol used by the JNI bridging layer
• Emits a compiler warning for any member that cannot be exported (unsupported signature, unexportable parameter type, etc.)

A member is exportable if it is non-private and all types in its signature are either built-in JNI-compatible types or other @jvm-annotated types.

@nonjvm

Excludes a specific member from JVM export. Use it to suppress the compiler warning that @jvm emits for unexportable members.

@jvm
class Parser {
    func parse(input: String) -> [Token] { ... }  // exported

    @nonjvm
    func parseInternal(buffer: UnsafeBufferPointer<UInt8>) { ... }  // excluded, no warning
}

@nonjvm has no runtime effect — it is a marker that tells the macro system to skip the annotated member.

@jvm_exported

Applied automatically by @jvm to exported properties. You do not apply this macro manually.

It generates the property getter (and setter for var properties) as separate JNI-registered functions so that the JVM proxy can access them individually.