table.unpack and Varargs

Part of the Introduction To Luau section of Coddy's Lua journey. Lesson 20 of 73.

Sometimes you have values in an array but need them as separate values — say, to pass each element as its own argument. That's table.unpack: it returns all the elements of an array, spread out.

local scores: {number} = {85, 92, 78}
print(table.unpack(scores))     -- 85  92  78  (one line, three values)
print(math.max(table.unpack(scores))) -- 92 — each element became an argument

The mirror image is varargs: a function that accepts any number of arguments via .... You've seen ... in Lua — Luau lets you type it, so every incoming value must match:

local function sum(...: number): number
    local total = 0
    for i = 1, select("#", ...) do
        total += select(i, ...)
    end
    return total
end

select("#", ...) returns how many arguments arrived, and select(i, ...) returns the arguments from position i onward — used as a single value in an expression, that's effectively "the i-th argument".

The two features click together: sum(table.unpack(scores)) spreads the array straight into the vararg function — Luau's answer to the spread-call pattern you'd see in other languages. table.unpack reads the array without modifying it.

Challenge

Easy

Create a typed array scores: {number} with 85, 92 and 78.

Print all the scores on one line using table.unpack.
Print the highest score using math.max and table.unpack.
Define local function sum(...: number): number that adds up all its arguments using select("#", ...) and select(i, ...), then print sum(table.unpack(scores)).
Print sum(10, 20) to show the same function works with plain arguments.

Try it yourself

-- Write code here
-- 1) declare scores: {number} = {85, 92, 78}
-- 2) print(table.unpack(scores)) and the math.max of the unpacked scores
-- 3) define sum(...: number): number with select, print sum(table.unpack(scores))
-- 4) print sum(10, 20)

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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