How are lambda functions implemented and operate at a low level within the system?

Lambda functions in Android (most often in Java or Kotlin) are implemented at a low level as objects that contain a reference to code and context (closure). In Java, the lambda compiler transforms lambda expressions into static methods and creates objects of functional interfaces, which delegate execution to these methods when called.

In Kotlin, lambdas are compiled into anonymous classes or use invoke methods, and can also capture variables from the surrounding context (closures), which are stored in the lambda object fields.

At the JVM bytecode level, lambda functions are often implemented via the invokedynamic mechanism, which allows dynamically creating objects of functional interfaces bound to specific code.

Example in Kotlin:

val sum = { a: Int, b: Int -> a + b }
println(sum(2, 3)) // 5

The compiler will create an object implementing a function with an invoke method, which executes the body of the lambda.