How to interface C++ and scripting languages

This example show how:

• Bind classes and functions to script engine
• Class instantiation and usage
• Derive classes and override functions in Javascript
• Exception handling

Full source: http://code.google.com/p/nasiu-scripting/source/browse/trunk/examples/nasiu/scripting/v8w/example1.cpp

Classes and functions binding

Our example class and functions definition:

class A
{
  int n_;

public:
  A();
  A(int n);
  virtual ~A();

  void method0();
  void method1(int a);
  int get_n() const;
  void set_n(int n);
};

int func1(A* a)
{
  std::cout << "func1 " << a->get_n() << std::endl;
  return a->get_n();
}

Adapt class for script:

 NASIU_V8W_ADAPT_CLASS(
   A, ,
   (int),
   (method0)
   (method1),
   ("n", get_n, set_n)
   ("n1", get_n, ));
 

Bind class and function to script engine:

using namespace nasiu::scripting;

script_engine<tags::v8w> se;
se.bind_class<A>();
se.bind_function("func1", func1);

Assign script scope variables:

se.set("var1", "var1-content");
se.set("var2", 10000);
se.set("var3", new A(84));

Instantiation and invocation

Use the function func1 and a script variable:

se.exec("func1(new A(var2))");

Instantiate A from Javascript and use in C++.

A* a1 = se.eval<A*>("new A(20)");

cout << "a1.n=" << a1->get_n() << endl;

Return the class from Javascript, instantiate, use, delete in C++:

class_type<tags::v8w, A> type_A = se.eval<class_type<tags::v8w, A> >("A");

A* a2 = type_A.new_instance(30);
cout << "a2.n=" << a2->get_n() << endl;

delete a2;

Function overriding

Override some functions of A in Javascript, return the class and use in C++:

class_type<tags::v8w, A> type_ExtA = se.eval<class_type<tags::v8w, A> >(
  "ExtA = function(n)"
  "{"
  "  var base = new A(n);"
  "  base.__proto__ = ExtA.prototype;"
  "  return base;"
  "};"
  "ExtA.prototype.__proto__ = A.prototype;"
  "ExtA.prototype.method1 = function(n)"
  "{"
  "  A.prototype.method1.call(this, n*n);"
  "};"
  "ExtA.prototype.method0 = function(n)"
  "{"
  "  A.prototype.method0.call(this);"
  "};"
  "ExtA"
);

A* a3 = type_ExtA.new_instance(40);
cout << "a3.n=" << a3->get_n() << endl;
cout << "a3.method0() "; a3->method0(); cout << endl;
cout << "a3.method1() "; a3->method1(40); cout << endl;

delete a3;

Exception handling

Define a Javascript function that throw a exception and catch it in C++:

function<tags::v8w> js_func = se.eval<function<tags::v8w> >(
  "(function (a, b)"
  "{"
  "  throw a + b;"
  "})"
);
try
{
  js_func.call<void>(10, 30);
}
catch (script_exception& e)
{
  cout << "js_func exception: " << e.what() << endl;
}

Catch C++ exceptions from Javascript:

void func2(int n)
{
  throw "native exception";
}
se.bind_function("func2", func2);

se.exec(
  "try "
  "{"
  "	func2(20);"
  "}"
  "catch (e)"
  "{"
  "  /* ... */"
  "};"
);