Tables with Functions

Part of the Object Oriented Programming section of Coddy's Lua journey — lesson 1 of 70.

In Lua, tables are incredibly versatile. Beyond storing data, they can also hold functions. This allows you to group related operations together, keeping your code organized and easy to manage.

To place a function inside a table, you simply assign it to a key just like any other value:

local myTable = {
    greet = function(name)
        return "Hello, " .. name
    end
}

print(myTable.greet("Alice"))  -- Output: Hello, Alice

You can also define the function separately and then add it to the table:

local myTable = {}

myTable.greet = function(name)
    return "Hello, " .. name
end

Or use this cleaner shorthand syntax:

local myTable = {}

function myTable.greet(name)
    return "Hello, " .. name
end

All three approaches produce the same result. You call the function using dot notation: myTable.greet("Alice"). This pattern of bundling functions with data is the foundation of object-oriented programming in Lua.

Challenge

Easy

Create a table named calculator that contains four arithmetic functions:

add(a, b) - returns the sum of a and b
subtract(a, b) - returns a minus b
multiply(a, b) - returns the product of a and b
divide(a, b) - returns a divided by b

You will receive three inputs:

An operation name (one of: add, subtract, multiply, divide)
First number
Second number

Call the appropriate function from your calculator table based on the operation name and print the result.

Cheat sheet

In Lua, tables can store functions alongside data. To add a function to a table, assign it to a key:

local myTable = {
    greet = function(name)
        return "Hello, " .. name
    end
}

print(myTable.greet("Alice"))  -- Output: Hello, Alice

You can also define functions separately and add them to the table:

local myTable = {}

myTable.greet = function(name)
    return "Hello, " .. name
end

Or use the shorthand syntax:

local myTable = {}

function myTable.greet(name)
    return "Hello, " .. name
end

Call table functions using dot notation: myTable.greet("Alice")

Try it yourself

-- Read inputs
local operation = io.read()
local num1 = tonumber(io.read())
local num2 = tonumber(io.read())

-- TODO: Create a calculator table with four functions:
-- add(a, b), subtract(a, b), multiply(a, b), divide(a, b)


-- TODO: Call the appropriate function from calculator table using the operation name
-- and print the result