Explain the internal implementation and mechanism of extension functions in the programming language.

In programming languages that support extensions, extension functions are implemented as additional modules that are connected to the main language or runtime environment.

The internal implementation of extension functions usually includes:

• Native code: functions written in a lower-level language (e.g., C or C++), which allows for increased performance and access to system resources.
• Binding interface: extensions provide an interface (API) through which the main language can invoke these functions, pass parameters, and receive results.
• Function registration: when the extension is loaded, functions are registered in the runtime environment so they can be called from the main language code.

Working mechanism:

1. When starting or on demand, the extension module is loaded.
2. The extension initializes, registering its functions.
3. When a function from the extension is called, control is transferred to the native code of the extension.
4. The function executes, utilizing the capabilities of the native code.
5. The result is returned back to the runtime environment and then to the calling code.

For example, in Android, extensions can be implemented via JNI (Java Native Interface), where Java code calls native functions in C/C++ for performance enhancement or access to system functions.