Example demonstrating that tail-call optimization in MRI Ruby allows for earlier garbage collection of unreachable objects.

gc_friendly_tco.rb

# Create some special classes to facilitate tracking allocated objects.
class TrackedArray < Array; end
class TrackedString < String; end
STRANG = "a" * 5000

# Other than a few extra escapes, the code below can be understood more or less
# as is.  Any weirdness is to facilitate interpretting with/without tail-call
# optimization in a DRY manner.
KLASS = <<-CODE
class GcFriendlyTco
  def calculate
    memory_hog
  end

  # Private because who knows what madness some libs are up to under the hood.
  private

  # Represents a method that does a bunch of memory intensive work before
  # returning an aggregate or some other type of result with a comparatively
  # small memory footprint.
  def memory_hog
    strs = TrackedArray.new
    30000.times { strs << TrackedString.new(STRANG) }
    char_count = 0
    strs.length.times {|i| char_count += strs[i].length }
    print_with_stats(char_count)
  end

  # Helper to print object allocation stats.
  def object_stats(tag)
    puts "\#{tag}:"
    puts "TrackedArray: \#{ObjectSpace.each_object(TrackedArray).count}"
    puts "TrackedString: \#{ObjectSpace.each_object(TrackedString).count}"
  end

  # Printer method serving as both the end of the tail-call chain and as the
  # provider of introspection.
  def print_with_stats(char_count)
    object_stats("Before GC")
    # Run the garbage collector.
    GC.start
    object_stats("After GC")
    puts char_count
  end
end
CODE

# Evaluate with TCO if the TCO environment variable is defined.
if ENV["TCO"]
  # Compilation with TCO requires the tco_method gem.
  require "tco_method"
  TCOMethod.tco_eval(KLASS)
else
  eval(KLASS)
end

GcFriendlyTco.new.calculate

# $ ruby memory_efficient_tco.rb
# Before GC:
# TrackedArray: 1
# TrackedString: 30000
# After GC:
# TrackedArray: 1
# TrackedString: 30000
# 150000000

# $ TCO=true ruby memory_efficient_tco.rb
# Before GC:
# TrackedArray: 1
# TrackedString: 30000
# After GC:
# TrackedArray: 0
# TrackedString: 0
# 150000000