Scripting with Lua - Game Coding Complete - page 355

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is used internally in some cases when accessing the leaf table is necessary. It s cur-

rently used by the ScriptProcess class in C++, which you ' ll see later in this
chapter.
The first thing the Create() function does is declare a local variable called obj .
This will be the instance table of the class. The next section will recursively call into
the Create() function of each base class in the inheritance chain, passing in the
construction data and the original leaf class (which is self the first time). When it
finally reaches the top base class, obj is initialized with either the construction-
Data table or an empty table if there is no construction data. After that, the metata-
ble is set up, and any overloaded operators defined in a special __operators table
are copied over. Finally, the object is returned.
Using the class() function is a breeze. Here

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s how you would define the Vec3 class

above:

Vec3 = class(nil,
{

x=0,y=0,z=0
})

function Vec3:Length()
return math.sqrt((self.x * self.x) + (self.y * self.y) + (self.z * self.z));
end

-- Create an instance of this class
V = Vec3:Create()

-- This version initializes the values
V2 = Vec3:Create({x = 10, y = 10, z = 10})

It doesn ' t get much easier than that! Later in this chapter, I ' ll even show you how you

can inherit from C++ classes.

Public/Private Variable Naming Conventions

One thing you can t easily get in Lua is a way to represent public, private, and

protected variables. A typical convention in many scripting languages is to put
an underscore in front of variable and function names that are meant to be
private, so seeing _var would let the programmer know that this variable is
meant to be private. Similarly, a function named _Update() would be a
private function.

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s good to have this kind of convention, or it quickly
becomes confusing what

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the public interface is. Refactoring can be a

nightmare.