Lambdas
Strict-arity procs.
Lambdas is a free Ruby Academy lesson on CoddyKit. This is lesson 3 of 4. Any 3 lessons of this learning path are free to read in full — after that, CoddyKit PRO unlocks every lesson, plus hands-on practice with a built-in code editor and a 24/7 AI tutor. It is part of the Ruby Academy learning path, and your progress syncs across the web and the CoddyKit app. The Ruby Academy course includes 4 lessons in total.
Strict-Arity Procs
A lambda is a special kind of Proc that behaves more like a regular method: it checks its argument count and treats return normally. Use it when you want predictable, method-like behavior.
square = lambda { |x| x * x }
puts square.call(6)The Stabby Lambda
The arrow syntax ->, nicknamed the 'stabby lambda,' is the most common way to write lambdas. Parameters go in parentheses.
add = ->(a, b) { a + b }
puts add.call(4, 5)Calling Lambdas
Lambdas support the same call styles as Procs: .call, .(), and [ ].
triple = ->(x) { x * 3 }
puts triple.call(2)
puts triple.(2)
puts triple[2]Strict Argument Checking
Unlike a Proc, a lambda raises ArgumentError if you pass the wrong number of arguments. This catches bugs early.
greet = ->(name) { "Hi #{name}" }
puts greet.call("Sam")
begin
greet.call
rescue ArgumentError => e
puts "Error: #{e.message}"
endreturn Stays Local
A return inside a lambda exits only the lambda, then execution continues. This matches how methods behave.
def demo
l = -> { return 10 }
l.call
20 # this runs
end
puts demoChecking for a Lambda
Both Procs and lambdas are instances of Proc. Ask lambda? to tell them apart.
l = ->(x) { x }
pr = proc { |x| x }
puts l.lambda?
puts pr.lambda?Lambdas with No Arguments
Omit the parentheses when a lambda takes no parameters.
now = -> { Time.now.year }
puts "Year: #{now.call}"Multi-line Lambdas
Lambdas can span multiple lines. The last expression is the return value.
classify = ->(n) {
return "zero" if n.zero?
n.positive? ? "positive" : "negative"
}
puts classify.call(0)
puts classify.call(-3)Passing Lambdas to Methods
Like Procs, lambdas convert to blocks with &, so they slot into map, select, and friends.
doubler = ->(n) { n * 2 }
p [1, 2, 3].map(&doubler)Lambdas as Return Values
A method can build and return a lambda, letting you create specialized functions on the fly.
def multiplier(by)
->(n) { n * by }
end
times10 = multiplier(10)
puts times10.call(5)Putting It Together
Lambdas are strict, method-like Procs:
- Write with
lambda { }or->(args) { }. - They enforce arity and keep
returnlocal. - Use them when correctness matters or you build functions to return.
is_even = ->(n) { n.even? }
p [1, 2, 3, 4, 5, 6].select(&is_even)Quick Check
Test your understanding of lambdas.
Recap
You learned lambdas:
- A lambda is a strict Proc; write it as
->. - It enforces argument counts.
returnexits only the lambda.lambda?distinguishes it from a plain Proc.
area = ->(w, h) { w * h }
puts area.call(3, 4)
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Frequently Asked Questions
Is the “Lambdas” lesson free?
Yes — any 3 lessons of the Ruby Academy learning path, including “Lambdas”, are free to read in full here on the web. After that, CoddyKit PRO unlocks every lesson, plus interactive practice with a built-in code editor and a 24/7 AI tutor. The Ruby Academy course includes 4 lessons in total.
What will I learn in “Lambdas”?
Strict-arity procs. You practise Ruby Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Ruby Academy?
No prior experience is required. Ruby Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.
How long does the “Lambdas” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
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