How an SDK call reaches iOS and Android

device.lucent.ts

import { PLATFORM } from "lucent:platform";
import { UIDevice } from "lucent:ios/UIKit";
import { Build } from "lucent:android/android.os";
import { main } from "lucent:thread";

export async function model(): Promise<string> {
  if (PLATFORM === "ios") return main(() => UIDevice.current.model);
  else return Build.MODEL ?? "unknown";
}

See the C++

iOS

m_device.mm

// Generated by Lucent from device.lucent.ts. Do not edit.
#import <UIKit/UIKit.h>
#include <lucent/platform/ios.h>
#include "m_device.h"

#pragma push_macro("model")
#undef model

namespace lucent_app {

lucent::Promise<lucent::String> m_device::model() {
#line 7 "device.lucent.ts"
  {
    lucent::Fn<lucent::String()> v0_ = lucent::Fn<lucent::String()>([]() mutable -> lucent::String {
#line 7 "device.lucent.ts"
      lucent::NativeRef v0_ = lucent::objc::wrap([UIDevice currentDevice], "UIDevice.current");
      return lucent::objc::fromNSString([((UIDevice*)lucent::objc::unwrap(v0_)) model], "UIDevice.model");
    });
#line 7 "device.lucent.ts"
    lucent::Promise<lucent::String> v1_ = lucent::runOnMain(v0_);
    lucent::String v2_ = co_await v1_;
    co_return v2_;
  }
}

void m_device::init() {
}

}  // namespace lucent_app

#pragma pop_macro("model")

Android

m_device.cpp

// Generated by Lucent from device.lucent.ts. Do not edit.
#include <lucent/platform/android.h>
#include "m_device.h"

#pragma push_macro("model")
#undef model

namespace lucent_app {

lucent::Promise<lucent::String> m_device::model() {
#line 7 "device.lucent.ts"
  {
#line 8 "device.lucent.ts"
    lucent::Opt<lucent::String> v0_ = [&]() -> lucent::Opt<lucent::String> {
      JNIEnv* env = lucent::jni::env();
      lucent::jni::LocalFrame frame_(env);
      static jclass cls_ = lucent::jni::findClass("android/os/Build");
      static auto id_ = lucent::jni::staticField(cls_, "MODEL", "Ljava/lang/String;");
      auto r_ = env->GetStaticObjectField(cls_, id_);
      lucent::jni::check(env);
      return lucent::jni::fromJStringOpt(env, static_cast<jstring>(r_));
    }();
    bool v2_ = !v0_.has();
    lucent::String v5_{};
    if (v2_) {
      v5_ = LUCENT_STR("unknown");
    } else {
      v5_ = v0_.value();
    }
#line 8 "device.lucent.ts"
    co_return v5_;
  }
}

void m_device::init() {
}

}  // namespace lucent_app

#pragma pop_macro("model")

One module holds both platforms. Each platform's build compiles its own branch, and "See the C++" shows both results.

Where the types come from

The first time a module imports lucent:ios/UIKit or lucent:android/android.os, Lucent reads it from your installed Xcode or Android SDK. The result is cached in ~/.cache/lucent for that SDK version, so later builds reuse it.

• Android: any package of android.jar, and of the app's Gradle dependencies. Reading the jar takes a few hundred milliseconds.
• iOS: any framework of the SDK, and of the app's pods. A large framework such as UIKit takes about 40 seconds, once.
• lucent sdk prefetch reads them ahead of time. Without an SDK, that platform's imports are untyped and lucent build skips the platform, saying so.

What a call compiles to

• iOS: a message send with the SDK's own selector, in Objective-C++ compiled against the real headers. Enum values are checked against the SDK at compile time.
• Android: a JNI call. Class and member IDs are looked up once per call site, and local references are freed after each call.

What comes back

• SDK objects stay in native code. JavaScript never sees them, so return plain values.
• A Java exception becomes an error whose code is the exception's class. An NSError becomes an error whose code is domain:code.
• nil or null where the SDK promises a value throws a TypeError.
• APIs marked main-thread only, such as UIKit's, compile only inside main(), or in a block or protocol requirement the SDK calls on the main thread (LUCENT3006).