asbind20

C++20 AngelScript binding library powered by templates. It also provides tools for easy interoperability between the AngelScript and C++.

The name and API design are inspired by the famous pybind11 library.

Brief Examples

1. Binding Application Interfaces

class my_value_class
{
public:
    my_value_class() = default;
    my_value_class(const my_value_class&) = default;

    my_value_class(int val)
        : value(val) {}

    ~my_value_class() = default;

    my_value_class& operator=(const my_value_class&) = default;

    friend bool operator==(const my_value_class& lhs, const my_value_class& rhs)
    {
        return lhs.value == rhs.value;
    }

    friend std::strong_ordering operator<=>(const my_value_class& lhs, const my_value_class& rhs)
    {
        return lhs.value <=> rhs.value;
    }

    int get_val() const
    {
        return value;
    }

    void set_val(int new_val)
    {
        value = new_val;
    }

    int value = 0;
};

void add_obj_last(int val, my_value_class* this_)
{
    this_->value += val;
}

void mul_obj_first(my_value_class* this_, int val)
{
    this_->value *= val;
}

void set_val_gen(asIScriptGeneric* gen)
{
    my_value_class* this_ = (my_value_class*)gen->GetObject();
    int val = static_cast<int>(gen->GetArgDWord(0));
    this_->set_val(val);
}

Binding code

asIScriptEngine* engine = /* Get a script engine */;
asbind20::value_class<my_value_class>(
    engine, "my_value_class", asOBJ_APP_CLASS_CDAK | asOBJ_APP_CLASS_ALLINTS | asOBJ_APP_CLASS_MORE_CONSTRUCTORS
)
    // Default & copy constructor, destructor,
    // and assignment operator (operator=/opAssign)
    .common_behaviours()
    // The constructor my_value_class::my_value_class(int val)
    .constructor<int>("void f(int val)")
    // Generate opEquals for AngelScript using operator== in C++
    .opEquals()
    // Generate opCmp for AngelScript using operator<=> in C++
    .opCmp()
    // Ordinary member functions
    .method("int get_val() const", &my_value_class::get_val)
    // Automatically deducing calling conventions
    .method("void add(int val)", &add_obj_last)  // asCALL_CDECL_OBJLAST
    .method("void mul(int val)", &mul_obj_first) // asCALL_CDECL_OBFIRST
    .method("void set_val(int)", &set_val_gen)   // asCALL_GENERIC
    // Convert member pointer to property
    .property("int value", &my_value_class::value);

The binding helpers also support registering a reference type, an interface, or global functions, etc. to the AngelScript engine.
You can find more examples in src/ext/array.cpp and src/ext/stdstring.cpp.

2. Invoking a Script Function

The library can automatically convert arguments in C++ for invoking an AngelScript function. Besides, the library provides RAII classes for easily managing lifetime of AngelScript object like asIScriptContext.

• AngelScript side

string test(int a, int&out b)
{
    b = a + 1;
    return "test";
}

• C++ side

asIScriptEngine* engine = /* Get a script engine */;
asIScriptModule* m = /* Build the above script */;
asIScriptFunction* func = m->GetFunctionByName("test");
if(!func)
    /* Error handling */

// Manage script context using RAII
asbind20::request_context ctx(engine);

int val = 0;
auto result = asbind20::script_invoke<std::string>(
    ctx, func, 1, std::ref(val)
);

assert(result.value() == "test");
assert(val == 2);

You can find more examples in test/test_invoke.cpp.

3. Using a Script Class

The library provides tools for instantiating a script class. The script_invoke also supports invoking a method, a.k.a., member function.

Script class in AngelScript

class my_class
{
    int m_val;
    void set_val(int new_val) { m_val = new_val; }
    int get_val() const { return m_val; }
    int& get_val_ref() { return m_val; }
};

C++ code

asIScriptEngine* engine = /* Get a script engine */;
asIScriptModule* m = /* Build the above script */;
asITypeInfo* my_class_t = m->GetTypeInfoByName("my_class");

asbind20::request_context ctx(engine);

auto my_class = asbind20::instantiate_class(ctx, my_class_t);

asIScriptFunction* set_val = my_class_t->GetMethodByDecl("void set_val(int)");
asbind20::script_invoke<void>(ctx, my_class, set_val, 182375);

asIScriptFunction* get_val = my_class_t->GetMethodByDecl("int get_val() const");
auto val = asbind20::script_invoke<int>(ctx, my_class, get_val);

assert(val.value() == 182375);

asIScriptFunction* get_val_ref = my_class_t->GetMethodByDecl("int& get_val_ref()");
auto val_ref = asbind20::script_invoke<int&>(ctx, my_class, get_val_ref);

assert(val_ref.value() == 182375);

*val_ref = 182376;

val = asbind20::script_invoke<int>(ctx, my_class, get_val);
assert(val.value() == 182376);

Advanced Features

The asbind20 library also provides tools for advanced users. You can find detailed examples in extensions and unit tests.

1. Automatically Generating Generic Wrapper at Compile-Time

Generating generic wrapper by macro-free utilities.

// generic_wrapper<MyFunction, OriginalCallConv>();
asGENFUNC_t f1 = asbind20::generic_wrapper<&global_func, asCALL_CDECL>();
asGENFUNC_T f2 = asbind20::generic_wrapper<&my_class::method, asCALL_THISCALL>();

// Use `use_generic` tag to force generated proxies to use asCALL_GENERIC
asbind20::value_class<my_value_class>(...)
    .constructor<int>(asbind20::use_generic, "void f(int)")
    .opEquals(asbind20::use_generic);

2. Dispatching Function Calls Based on Type Ids

This feature is similar to how std::visit and std::variant works. It can be used for developing templated container for AngelScript.

asbind20::visit_primitive_type(
    [](auto val)
    {
        using type = decltype(val);

        if constexpr(std::is_same_v<type, int>)
        {
            // play with int
        }
        else if constexpr(std::is_same_v<type, float>)
        {
            // play with float
        }
        else
        {
            // ...
        }
    },
    as_type_id, // asTYPEID_BOOL, asTYPEID_INT32, etc.
    ptr_to_val // void* to value
);

You can find example usage in src/ext/array.cpp.

Supported Platforms

• CMake >= 3.20
• AngelScript >= 2.37.0
• Any C++ compiler that supports C++20.
  Currently, this library has been tested by MSVC 19.41 on Windows and GCC 12 on Linux.

How to Use

Follow the tutorial of AngelScript to build and install it at first, or use a package manager like vcpkg.

A. Build and Install

Build and install the library.

cmake -GNinja -DCMAKE_BUILD_TYPE=Release -S. -B build
cmake --build build
cmake --install build

Use the library in a CMakeLists.txt.

find_package(asbind20 REQUIRED)

target_link_libraries(main PRIVATE asbind20::asbind20)

You can find a detailed example in test/test_install/.

B. As Submodule

Clone the library into your project.

git clone https://github.com/HenryAWE/asbind20.git

Use the library in a CMakeLists.txt.

add_subdirectory(asbind20)

target_link_libraries(main PRIVATE asbind20::asbind20)

You can find a detailed example in test/test_subdir/.

License

MIT License