Question

I’m just diving into Procs, blocks, and lambdas. I’m noodling around trying different things, but I’m unsure as to why this doesn’t work:

def iterate(ary, &code)
  ary.each_with_index do |n, i|
    ary[i] = code.call(n)
  end
end

iterator = Proc.new do |n|
  n ** 2
end

p iterate([1,2,3], iterator)

# `iterate': wrong number of arguments (2 for 1) (ArgumentError)

Answer 1

That’s because & symbol before the last method’s parameters is intended for explicit definition of block as parameter.

In your case you have 2 ways:
1) Use proc parameter instead of block:

def iterate(ary, code)
  ary.each_with_index do |n, i|
    ary[i] = code.call(n)
  end
end

iterator = Proc.new do |n|
  n ** 2
end

p iterate([1,2,3], iterator)  # => [1, 4, 9]

or 2) Use block instead of proc creation:

def iterate(ary, &code)
  ary.each_with_index do |n, i|
    ary[i] = code.call(n)
  end
end

p iterate([1,2,3]) { |n| n ** 2 }  # => [1, 4, 9]