./bin/crystal test.cr --release
Error in ./src/fiber.cr:26: this 'initialize' doesn't explicitly initialize instance variable '@stack_top' of Fiber, rendering it nilable

Empty enumerable (Enumerable::EmptyError)
[4312558] ???
[4312118] ???
[4308862] main +11918
[140672253235013] __libc_start_main +245
[4249449] ???
[0] ???

require "benchmark"

class Testeroo1
  def initialize
    @flags = [] of String
  end

  def append_flag(flag, description)
    @flags << "    #{flag}#{" " * (33 - flag.size)}#{description}"
  end
end

class Testeroo2
  def initialize
    @flags = [] of String
  end

  def append_flag(flag, description)
    @flags << String.build do |str|
      str << "    "
      str << flag
      (33 - flag.size).times do
        str << " "
      end
      str << description
     end
  end
end

Benchmark.ips(warmup: 4, calculation: 10) do |r|
  r.report("New") do
    test = Testeroo1.new
    5.times do
      test.append_flag "-f", "a test flag to figure out how fast things are"
    end
  end
  r.report("Old") do
    test = Testeroo2.new
    5.times do
      test.append_flag "-f", "a test flag to figure out how fast things are"
    end
  end
end

New 421.11k (± 8.33%)       fastest
Old  288.8k (± 5.66%)  1.46× slower