Using Operator Overloading for Math

When programming, there are many occasions where one wants to define addition/multiplication and different kinds of operations for a mathematical object. For example, one might define a vector or matrix and some addition/subtraction/multiplication functions to go with it.

Vector3 Struct Definition

One can define a Vec3 in the following way:

Vec3 :: struct {
    x: float;
    y: float;
    z: float;
}

We use x, y, z to represent the 3D coordinates.

Vector Addition

Given the above definition, one can overload the addition operator as follows:

operator + :: (a: Vec3, b: Vec3) -> Vec3 {
    c: Vec3;
    c.x = a.x + b.x;
    c.y = a.y + b.y;
    c.z = a.z + b.z;
    return c;
}

This is a short example demonstrating vector addition:

a := Vec3.{1, 2, 3};
b := Vec3.{3, 4, 5};
c := a + b;
print("c = %\n", c);

Vector Subtraction

Here is how one can overload the subtraction operator for Vec3.

operator - :: (a: Vec3, b: Vec3) -> Vec3 {
    c: Vec3;
    c.x = a.x - b.x;
    c.y = a.y - b.y;
    c.z = a.z - b.z;
    return c;
}

This is a short example demonstrating vector subtraction:

a := Vec3.{1, 2, 3};
b := Vec3.{3, 4, 5};
c := a - b;
print("c = %\n", c);

Vector Negation

Here is how one can overload the negation operator for Vec3.

operator - :: (a: Vec3) -> Vec3 {
    b: Vec3;
    b.x = -a.x;
    b.y = -a.y;
    b.z = -a.z;
    return b;
}

This is a short example demonstrating vector negation:

a := Vec3.{1, 2, 3};
b := -a;
print("b = %\n", b);

Vector Scalar Multiplication

One can overload the multiplication operator so that Vec3 can support scalar multiplication. We can attach the #symmetric keyword to the function so that the scalar float value is swappable with the Vec3; in this way, we do not need to define two different functions to represent scalar multiplication.

operator * :: (a: Vec3, b: float) -> Vec3 #symmetric {
    c: Vec3 = a;
    c.x *= b;
    c.y *= b;
    c.z *= b;
    return c;
}

When we compile the example below, the ordering of the Vec3 and scalar float value does not need matter.

a: Vec3 = Vec3.{1, 2, 3};
b: float = 3.0;
c := a * b; 
d := b * a; // <- perform commutative scalar multiplication 
print("c = %\n", c);
print("d = %\n", d);

Vector Dot Product

Dot Product for Vec3 can be written as follows:

dot :: (a: Vec3, b: Vec3) -> float {
    c := (a.x * b.x) + (a.y * b.y) + (a.z * b.z);
    return c;
}

This is a short example demonstrating dot product:

a := Vec3.{1, 2, 3};
b := Vec3.{2, 4, 6};
c := dot(a, b);
print("c = %\n", c); // <- answer should be 'c = 28.0'

Matrix Struct Definition

There are many possible implementations of a matrix that have many pros and cons. This is one possible implementation of a matrix.

Matrix :: struct(M: int, N: int) {
    data: [M][N] float;
}

In this definition, a matrix is a 2D array of data, which takes M and N as a parameter for the struct for the rows and columns of the matrix, respectively.

Matrix Addition

Given the definition, one can implement matrix addition by adding up the corresponding elements between matrix A and matrix B to get matrix C.

operator + :: (a: Matrix($M, $N), b: Matrix(M, N)) -> Matrix(M, N) {
    c: Matrix(M, N);
    for i : 0..(M-1) {
        for j : 0..(N-1) {
            c.data[i][j] = a.data[i][j] + b.data[i][j];
        }
    }
    return c;
}

Matrix Subtraction

Given the definition, one can implement matrix subtraction by subtracting the corresponding elements between matrix A and matrix B to get matrix C.

operator - :: (a: Matrix($M, $N), b: Matrix(M, N)) -> Matrix(M, N) {
    c: Matrix(M, N);
    for i : 0..(M-1) {
        for j : 0..(N-1) {
            c.data[i][j] = a.data[i][j] - b.data[i][j];
        }
    }
    return c;
}