08-functions.md

Functions

Define and Call

def greet(name)
  puts "Hello, #{name}!"
end

greet("World")

No-Argument Functions

Functions with no parameters can omit the parentheses in the definition:

def say_hello
  puts "Hello!"
end

say_hello

Both def say_hello and def say_hello() are valid — the () is optional when there are no parameters.

Return Values

The last expression in a function body is implicitly returned:

def add(a, b)
  a + b
end

puts add(2, 3)   # 5

Use explicit return for early exits:

def classify(x)
  if x > 10
    return "big"
  end
  "small"
end

puts classify(5)    # small
puts classify(20)   # big

Parenthesis-Free Calls

When calling with arguments, parentheses are optional:

puts "hello"
greet "World"

Recursion

def factorial(n)
  if n <= 1
    return 1
  end
  n * factorial(n - 1)
end

puts factorial(5)   # 120

Default Parameter Values

Parameters can have default values. Callers can omit trailing arguments, and the defaults kick in:

def greet(name, greeting = "Hello")
  puts "#{greeting}, #{name}!"
end

greet("Alice")            # Hello, Alice!
greet("Alice", "Hey")     # Hey, Alice!

Multiple defaults and various expressions are supported:

def connect(host, port = 8080, tls = true)
  puts "#{host}:#{port} tls=#{tls}"
end

connect("example.com")              # example.com:8080 tls=true
connect("example.com", 443)         # example.com:443 tls=true
connect("example.com", 443, false)  # example.com:443 tls=false

All parameters can be optional:

def label(text = "default", color = nil)
  puts text
end

label()          # default
label("hello")   # hello

Required parameters must come before parameters with defaults — mixing them the other way is a compile error.

---

Next: Lambdas