Tweak comments on Property#null_object?

[amomchilov]

Clarify what the (class << object; self; end) trick does.

I also split apart the large comment into what is (IMO) a more readable form. WDYT?

[amomchilov]

Could you merge this? Only you have access

[amomchilov]

Reflecting on this, I was curious about using the bind_call trick to translate the method over from Kernel. Turns out it's a bit slower:

#!/usr/bin/ruby

# Calculating -------------------------------------
#     #singleton_class     30.646M (± 1.2%) i/s -    155.427M in   5.072506s
#            bind_call      9.594M (± 4.7%) i/s -     48.233M in   5.043490s
#             class <<     20.887M (± 1.1%) i/s -    104.728M in   5.014629s

require "benchmark/ips"

o = Object.new
SINGLETON_CLASS_METHOD = Kernel.instance_method(:singleton_class)

Benchmark.ips do |x|
  x.config(warmup: 0.1, time: 5)

  x.report("#singleton_class") do |times|
  i = 0
    while (i += 1) < times
      o.singleton_class
    end
  end

  x.report("bind_call") do |times|
    i = 0
    while (i += 1) < times
      SINGLETON_CLASS_METHOD.bind_call(o)
    end
  end

  x.report("class <<") do |times|
    i = 0
    while (i += 1) < times
      class << o; self; end
    end
  end
end