Sams Teach Yourself Ruby in 21 Days

Block Scope for Local Variables

Variable assignment inside a block can have a surprising effect if you're not careful. The following code ought to find a nutrient in a list, such that the amount supplied (as indicated by the hash value) is at least 100%, but it doesn't work very well:

label = {'Folicin'=>106, 'Vitamin A'=>146, 'Thiamine'=>94}
label.each do |nutrient, percent|
  last_full_rda = nutrient if percent >= 100
end

puts last_full_rda  # error: "undefined local variable"

Since last_full_rda first appears within the do...end block associated with each, its scope is limited to that block. (Not all code enclosures have this property. We'll earn a more intimate understanding of blocks on Day 14.) Making an assignment to last_full_rda above ...