This is Part 2.5 of my Integrating Lua into C++ Tutorial series.

Local c = ' 0,0,0, '. Dim or 0.75)-true means lock the background against touches: T. DimScreen (nil, c, nil, true)-forward declaration for the text field: local field-forward reference (needed for Lua closure) for the input textfield (or textbox) local field, numberField. This section describes the C API for Lua, that is, the set of C functions available to the host program to communicate with Lua. All API functions and related types and constants are declared in the header file lua.h. Even when we use the term 'function', any facility in the API may be provided as a macro instead. Lua 5.4 Reference Manual The reference manual is the official definition of the Lua language. For a complete introduction to Lua programming, see the book Programming in Lua.

This is an extension of Part 2. Here, we will extend the ScriptObject class to provide better functionality

This part of the tutorial uses a lot of templates. Please touch up on that before continuing on with the tutorial.

The important things you should take note before coming back would be:

Templated Functions
Specialized Templated Functions
Variadic templates

What the hell, I’ll touch a bit upon the topic, at least some parts of it that he needs, but you really should properly learn about templates.

Lua Textbox Codes

Short lesson on Templates

The topic of templates is a huge beast. I won’t be covering the whole topic, and I won’t be going in depth as I will only be covering enough materials to be used in this tutorial.

I will mostly be covering templates for functions, as well as variadic templates.

The code snippet above is a simple templated function that takes in a value of any type, convert it to string, and then print it out.

If you run the code successfully, you should get:

Value: 3

It behaves just like:

The compiler is able to deduce that when we inserted ‘num’ as the argument, the desired parameter type is integer. It then instantiates a new function with the desired value type.

Lua Textbox Chat

The function above is just a normal function. In the event that a string is passed in as an argument, it will call this function instead of the default templated function.

The function above is a variadic templated function. In layman terms, this function can take multiple amount of arguments and convert it into a format usable as input for our Lua functions.

The thing about our usage is that it works in a recursive manner, in which a variable is ‘processed’ in every recursion, and removed from the parameter pack. It will continue on until there’s no more arguments and will call the empty function.

Due to that, we have to define an empty function with the same name.

Let’s consolidate all those and try it out.

If you run the code successfully, you should get:

Value: 3,’test’,5.400000

New ScriptObject Class

Let’s start implementing it into our ScriptObject class.

The main difference between the new and the old ScriptObject class lies with the constructor and the CallFunction function. Both of these functions now takes in a variadic number of arguments, which will then be sent into their respective Lua functions.

I also added a get, tryGet, and set function for the Lua class’ member variables.

Now let’s create a new Lua class in our trusty ‘TestClass.lua’ named ‘TestClass2’ that takes in an argument in it’s constructor, as well as a function that takes in an input and returns the value after manipulating it.

Lua Textbox Code

Now Let’s try this out!

If all goes well, you should get:

TestClass2 Created with Input (5,’test’)!
TestClass2 TestFunction Called with Input (3, 7)!
Return Value: 10
numValue: 5
strValue: test

Summary

This new ScriptObject class would allow for an easy use to all the functionalities required of an OOP Lua class in C++. As always, the code above was edited and filled only with the bare minimum functionality for the sake of simplicity. The more complete codebase will be posted below, as usual.

But seriously though, if this article is the first exposure you have to templates, please go search up on a better tutorial because that isn’t the main scope of this tutorial. The information I provided is just the bare minimum needed for the tutorial. Template Programming is a huge beast, that is beneficial to learn for any C++ programmer.

Codes

TestClass.lua

ScriptObject.hpp

ScriptObject.cpp

ConvertArgsToLuaArgs.hpp

Main.cpp