Iterators (.each)

Relax. We'll talk through this in plain words — no textbook voice.

Iterators are hugely important in idiomatic Ruby code. .each, .map, and .select let you work with items in an array or hash in a way that's readable and clear.

ruby

prices = [100, 250, 400]

prices.each do |price|
  puts "Price: #{price} yen"
end

tax_included = prices.map do |price|
  price * 1.1
end

puts tax_included

each runs a block once for every item. map transforms each item and returns a brand-new array.

You should see

Price: 100 yen Price: 250 yen Price: 400 yen 110.00000000000001 275.0 440.00000000000006

Info

A handy rule of thumb: reach for map when you want new data back, and each when you just want to produce output.

Easy traps

Float precision can cause issues with money calculations. In real payment systems, it's better to store amounts like yen or cents as integers.