Function Parameters in Lua

In the previous lesson, you defined and called a simple function with no inputs. As a quick reminder, that function ran the same way every time because it had no data coming in. In this lesson, you will learn how to make your functions flexible by giving them parameters — placeholders that accept information when the function is called. This is how you customize a function’s behavior.

-- Define a function to greet the user by name
local function greet_user_by_name(name)
    print("Hello, " .. name .. "!")
end

Explanation:

• The comment states the function’s purpose.
• local function greet_user_by_name(name) defines a function and introduces a parameter named name. This parameter is a placeholder for the value you will pass in later.
• print("Hello, " .. name .. "!") builds the message using the string concatenation operator .. to combine text and the parameter value.
• end closes the function.

-- Call the function
greet_user_by_name("Alex")

Explanation:

• We call greet_user_by_name and pass "Alex" as the argument. The argument fills the name parameter inside the function.
• When this line runs, the function prints: Hello, Alex!
• Try running this in CodeSignal to see the output immediately.

Lua does not support default parameter values directly in the function definition like some other languages. However, you can easily set a default value inside the function body using the or operator.

-- Define a function with a default value for the parameter
local function greet_user_by_name(name)
    name = name or "Guest"
    print("Hello, " .. name .. "!")
end

Explanation:

• name = name or "Guest" checks if name is nil or false. If so, it assigns "Guest" as the default value.
• Now, if you call greet_user_by_name() without an argument, it will greet "Guest".

Example calls:

greet_user_by_name("Alex")   -- Output: Hello, Alex!
greet_user_by_name()         -- Output: Hello, Guest!

This pattern allows you to provide default values for parameters in your Lua functions.