Extending Shapes

Part of the Introduction To Luau section of Coddy's Lua journey — lesson 41 of 73.

Related shapes often share fields. Every Admin is also a User; copying the shared fields into both declarations invites them to drift apart.

You met the intersection operator & when combining aliases — it works exactly the same for shapes. A & B means "has everything from A and everything from B":

type User = {name: string, age: number}
type Admin = User & {level: number}

-- Admin now requires: name, age AND level
local root: Admin = {name = "Root", age = 35, level = 9}

Where TypeScript needs a separate extends keyword for interfaces, Luau needs nothing new — intersections already do the job. You can chain several parts:

type Contact = {email: string}
type Developer = User & Contact & {yearsExperience: number}

Don't confuse & with |: a union A | B is either shape, while an intersection A & B must satisfy both at once. And since Admin has every User field, an Admin value can be passed anywhere a User is expected.

Challenge

Easy

Create these type aliases:

Employee — id (number), name (string), department (string)
Manager — Employee extended (via &) with teamSize (number)
Contact — email (string)
Developer — the intersection of Employee, Contact and {yearsExperience: number}

Create:

teamLead of type Manager — id 101, name "Alice Johnson", department "Engineering", teamSize 8
dev of type Developer — id 102, name "Bob Smith", department "Engineering", email "bob@company.com", yearsExperience 5

Create a function getManagerSummary that takes a Manager and returns [name] manages [teamSize] people.

Print, each on its own line:

the result of getManagerSummary(teamLead)
[name] has [yearsExperience] years of experience for dev
the department of teamLead
the email of dev

Try it yourself

-- Write code here
-- 1) define Employee, then Manager / Contact / Developer with &
-- 2) create teamLead and dev
-- 3) write getManagerSummary
-- 4) print the four requested lines

Test yourself

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

Extending Shapes

All lessons in Introduction To Luau