Operator Overloading

Suppose we have two objects that belong to a custom Vector class, how would we allow the addition of those two objects? Using normal class functions would be good, but it would take a longer time to write, and would be harder to understand.

To solve this issue in Class++, just like in C++, we can change the way operators work for our classes. This is known as operator overloading.

local class = ClassPP.class

local Vector = class "Vector3" {
    constructor = function(self, x: number, y: number, z: number)
        if typeof(x) ~= "number" or typeof(y) ~= "number" or typeof(z) ~= "number" then self.coordinates = {0, 0, 0} return end
        self.coordinates = {x, y, z}
    end,
    Public = {
        coordinates = {0, 0, 0},
    },
}

function Vector.Public:operator_add(otherVector)
    assert(#self.coordinates == #otherVector.coordinates)

    local coordinates = {}

    for i = 1, #self.coordinates do
        coordinates[i] = self.coordinates[i] + otherVector.coordinates[i]
    end

    return Vector.new(coordinates[1], coordinates[2], coordinates[3])
end

function Vector.Public:__tostring()
    return "(" .. table.concat(self.coordinates, ", ") .. ")"
end

local vector1 = Vector.new(4, 5, 2)
local vector2 = Vector.new(1, 2, 3)

print(vector1 + vector2) -- Prints "(5, 7, 5)"

In this example, we have created a custom Vector3 class that has a special function called operator_add, this special function is one of the special functions in Class++ that allows you to overload a specific operator. Here, we overloaded the operator + with our custom function that allows us to add two Vectors together.

Overloadable Operators

Method	Description
`operator_add(self, obj)`	Function for overloading the + operator.
`operator_sub(self, obj)`	Function for overloading the - operator.
`operator_mul(self, obj)`	Function for overloading the * operator.
`operator_div(self, obj)`	Function for overloading the / operator.
`operator_idiv(self, obj)`	Function for overloading the // operator.
`operator_mod(self, obj)`	Function for overloading the % operator.
`operator_pow(self, obj)`	Function for overloading the ^ operator.
`operator_unm(self)`	Function for overloading the unary – operator.
`operator_eq(self, obj)`	Function for overloading the == operator.¹
`__tostring()`	Fired when tostring is called on the object.

Info

¹: This function will only run when == operator is used with the same base type (table, userdata, etc.). It will not work with different types, such as an object with a table, or another type.

Warning

Trying to directly call the operator functions will result in an error. They must be called with their operators.