require 'YAML'
require 'benchmark'
 
# Case 1: Global variable
 
GlobalConfig = {}
 
def get()
  if GlobalConfig[:config]
    return GlobalConfig[:config]
  else
    data = File.open('config.yml')
    GlobalConfig[:config] = YAML.load(data) #  dynamic constant assignment error
    return GlobalConfig[:config]
  end  
end
 
# Case 2: Instance variable
 
class ConfigReader
  def initialize(name)
    @name = name
  end
  
  def config
    @config ||= get_from_disk
  end
 
  def get_from_disk
    data = File.open('config.yml')
    YAML.load(data)
  end
end
 
config_reader = ConfigReader.new('config.yml')
 
# Case 3: Lambda
 
Config = lambda{
  data = File.open('config.yml')
  config = YAML.load(data)
}.call
 
# Benchmark
 
n = 1000000
Benchmark.bm() do |x|
  x.report("Case 1.a: Global variable   ") { n.times do   ; get; end }
  x.report("Case 1.b: Global variable   ") { n.times do   ; GlobalConfig[:config]; end }
  x.report("Case 2  : Instance variable ") { n.times do   ; config_reader.config; end }
  x.report("Case 3  : Lambda            ") { n.times do   ; Config; end }
end
 
# Result
#       user     system      total        real
# Case 1.a: Global variable     0.670000   0.010000   0.680000 (  0.750651)
# Case 1.b: Global variable     0.250000   0.000000   0.250000 (  0.270964)
# Case 2  : Instance variable   0.330000   0.000000   0.330000 (  0.376627)
# Case 3  : Lambda              0.120000   0.010000   0.130000 (  0.153685)