Mastering Ruby Closures

Blocks as Closures and Block Local Variables

In Ruby, blocks act like anonymous functions. After all, blocks carry a bunch of code, to be called only when yielded. A block also carries around the context in which it was defined:

def chalkboard_gag(line, repetition)
  repetition.times { |x| puts "#{x}: #{line}" }
end

chalkboard_gag("I will not drive the principal's car", 3)

This returns:

0: I will not drive the principal's car
1: I will not drive the principal's car
2: I will not drive the principal's car

What’s the free variable here? It is line. That’s because line is not a block local variable. Instead, it needs access to the outer scope until it reaches the arguments of chalkboard_gag.

The behavior of the ...