Array that does not let you mutate while inside an `each` block

immutable_each_array.cr

class ImmutableEachArray(T)
  include Enumerable(T)

  @iterating = Atomic(Int32).new(0)
  @array = Array(T).new

  def <<(value : T) : self
    raise CannotMutateWhileIterating.new("you iteratin bruh") if @iterating.get > 0

    @array << value
    self
  end

  def each
    @iterating.add 1
    @array.each { |i| yield i }
  ensure
    @iterating.sub 1
  end

  class CannotMutateWhileIterating < Exception
  end
end