add-lua-binding-simple

Development

Add simple Cataclysm-BN Lua bindings for string_id types, enums, and basic read-only C++ types. Use when exposing straightforward C++ types to Lua.

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Add Simple Lua Binding

This skill helps you add Lua bindings for simple C++ types like string_id, enums, or basic classes.

What You'll Do

Identify the type you want to bind (e.g., my_type, my_enum)
Choose the binding file (usually src/catalua_bindings_ids.cpp for IDs, or a relevant catalua_bindings_*.cpp)
Add Luna documentation macro to src/catalua_luna_doc.h
Register the binding in the appropriate function
Build and test the changes

Step-by-Step Instructions

For string_id types

// In src/catalua_luna_doc.h, add:
LUNA_ID( my_type, "MyType" )

// In src/catalua_bindings_ids.cpp, in reg_game_ids():
reg_id<my_type, has_int_id>( lua );
// Use true if type has int_id, false otherwise

For enum types

// In src/catalua_luna_doc.h, add:
LUNA_ENUM( my_enum, "MyEnum" )

// In appropriate catalua_bindings_*.cpp file:
{
    auto values = sol::initializers(
        "VALUE_ONE", my_enum::VALUE_ONE,
        "VALUE_TWO", my_enum::VALUE_TWO
    );
    luna::set_enum( lua, values );
}

Note: Use trailing return types and auto throughout (see patterns below).

For simple data types (read-only)

// In src/catalua_luna_doc.h, add:
LUNA_DOC( my_class, "MyClass" )

// In appropriate catalua_bindings_*.cpp:
#define UT_CLASS my_class
{
    auto ut = luna::new_usertype<UT_CLASS>(
        lua,
        luna::no_bases,
        luna::no_constructor
    );

    // Add members
    SET_MEMB( my_field );      // Mutable field
    SET_MEMB_RO( const_field ); // Read-only field
    SET_FX( my_method );        // Method
}
#undef UT_CLASS

Important Patterns

Documentation Comments

DOC( "Description of the type" );
DOC( "Additional details about usage" );

Member Macros

SET_MEMB(name) - Mutable member variable or property
SET_MEMB_RO(name) - Read-only member
SET_FX(name) - Member function
SET_FX_T(name, signature) - Member function with specific overload

Luna Macros

LUNA_ID(CppType, "LuaName") - For string_id/int_id pairs
LUNA_DOC(CppType, "LuaName") - For documentation-only types
LUNA_ENUM(CppType, "LuaName") - For enum types
LUNA_VAL(CppType, "LuaName") - For value types
LUNA_PTR_VAL(CppType, "LuaName") - For pointer types

Testing

After adding bindings:

# Build
cmake --build --preset linux-full --target cataclysm-bn-tiles

# Test in Lua console (debug menu -> Lua console)
local my_id = MyTypeId.new("some_id")
print(my_id:str())
print(my_id:is_valid())

Common Issues

Linker errors: Make sure the type header is included
Missing comparison operators: Some types need operator== and operator<
Build errors: Check macro syntax and semicolons

Files to Modify

src/catalua_luna_doc.h - Add LUNA_* macro
src/catalua_bindings_ids.cpp - For ID types
src/catalua_bindings_*.cpp - For other types (choose appropriate file)

References

Lua Integration Docs: docs/en/mod/lua/explanation/lua_integration.md
Existing Examples: src/catalua_bindings_ids.cpp
Luna System: src/catalua_luna.h