TopolearnMethods are the unit of reuse in Ruby, and keyword arguments are the idiomatic way to keep call sites readable.
Define a method with def name(params) ... end. The value of the last expression is returned automatically; return is only needed to exit early. Endless methods (Ruby 3.0) fit one-liners: def square(x) = x * x.
Parameter kinds, in the order they must appear:
- Required positional:
def greet(name). - Optional with a default:
def greet(name, greeting = "Hello"). - Splat
*argscollects extra positional arguments into an array. - Keyword arguments:
def connect(host:, port: 5432).host:is required,port:optional. Callers writeconnect(host: "db", port: 6543), which is self-documenting and order-independent. Missing or unknown keywords raiseArgumentError. - Double splat
**optscollects extra keywords into a hash. - A block parameter
&block(covered with blocks).
Since Ruby 3.0, positional and keyword arguments are strictly separated: a hash passed positionally is no longer silently converted to keywords. Spread one explicitly with **hash.
Method names may end in ? (predicates), ! (dangerous or in-place) or = (setters). A method defined at the top level of a script becomes a private method on Object, callable anywhere in that script.
Methods can return multiple values as an array, which callers destructure: min, max = bounds(list).
Example
def greet(name, greeting = "Hello", punct: "!")
"#{greeting}, #{name}#{punct}"
end
def connect(host:, port: 5432, **opts)
"#{host}:#{port} #{opts}"
end
def bounds(list) = [list.min, list.max]
puts greet("Ada") # Hello, Ada!
puts greet("Bo", "Hi", punct: "?") # Hi, Bo?
puts connect(host: "db", ssl: true) # db:5432 {ssl: true}
settings = { host: "cache", port: 6379 }
puts connect(**settings) # cache:6379 {}
low, high = bounds([4, 9, 1])
puts "#{low}..#{high}" # 1..9
begin
connect(port: 1)
rescue ArgumentError => e
puts e.message # missing keyword: :host
endRemember
- The last expression is the return value
- Keyword arguments (name:) make calls self-documenting
- Spread hashes into keywords explicitly with **
Watch out for
- Passing a hash where keywords are expected without ** in Ruby 3, causing ArgumentError.