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Control Flow in Ruby

Essential branching and looping constructs with readable idioms.

if / elsif / else

Conditions use truthiness: only false and nil are falsy; everything else is truthy.

if n > 0
  :pos
elsif n == 0
  :zero
else
  :neg
end

Note: It’s elsif (one word), not else if.

unless and postfix modifiers

unless expresses negative conditions clearly. Postfix modifiers make short guards concise.

unless ready
  prepare
end

do_something if ready
log("oops") unless ok

case / when

case uses === under the hood, enabling ranges, regexes, and class checks.

case status
when 200..299 then :ok
when 404      then :not_found
when /5\d\d/  then :server_error
when String   then :string_input
else               :error
end

Short‑circuit boolean control

Use && and || to guard or default values.

user && user.login!      # only if user is truthy
name = input || "guest"  # default if input is nil/false

Loops and iterators

Prefer iterators to manual loops; while/until exist when you need them. Control with break, next, and redo.

i = 0
while i < 3
  puts i
  i += 1
end

3.times { |k| puts k }
[1,2,3].each { |v| puts v }
1.upto(3) { |v| puts v }

Ternary and statement modifiers

Use ternary for small expression‑level choices; keep branches short. Modifiers keep guards succinct.

ok ? "yes" : "no"
puts("done") if ok

Summary

  • Prefer iterators (times, each, upto) over manual loops when possible
  • Use postfix modifiers and short‑circuiting for clear, concise control flow
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