Do you know what de-duplication is?

Desugaring is the process of converting syntactic sugar (high-level syntactic constructs that make code easier to write) into lower-level, more primitive constructs that are easier for the compiler or runtime environment to process.

Examples in Android development (Java/Kotlin):

• Lambda expressions:

  // Syntactic sugar: lambda
  Runnable r = () -> System.out.println("Hello");
  

  Desugaring transforms this into an anonymous class:

  // Desugaring: anonymous class
  Runnable r = new Runnable() {
      @Override
      public void run() {
          System.out.println("Hello");
      }
  };
  

• for-each loops:

  // Syntactic sugar: for-each
  List<String> list = Arrays.asList("a", "b");
  for (String s : list) {
      System.out.println(s);
  }
  

  Desugaring transforms this into an iterator loop:

  // Desugaring: iterator loop
  List<String> list = Arrays.asList("a", "b");
  for (Iterator<String> it = list.iterator(); it.hasNext(); ) {
      String s = it.next();
      System.out.println(s);
  }
  

• Coroutines in Kotlin (in earlier implementations):

  // Syntactic sugar: suspending function
  suspend fun fetchData(): String {
      delay(1000)
      return "Data"
  }
  

  Desugaring (for example, via state machine generation) transforms this into lower-level code.

Desugaring is important because it:

• Allows the use of more expressive and concise constructs (sugar) without complicating the compiler/runtime implementation.
• Ensures backward compatibility, as desugared code can run on older platform or VM versions.
• Simplifies code analysis and optimization for the compiler.

In Android, desugaring is actively used by JVM/ART and build tools (e.g., D8/R8).