Ruby: Proc#call vs yield

Question

What are the behavioural differences between the following two implementations in Ruby of the thrice method?

module WithYield
  def self.thrice
         


        

Answer 1

The other answers are pretty thorough and Closures in Ruby extensively covers the functional differences. I was curious about which method would perform best for methods that optionally accept a block, so I wrote some benchmarks (going off this Paul Mucur post). I compared three methods:

• &block in method signature
• Using &Proc.new
• Wrapping yield in another block

Here is the code:

require "benchmark"

def always_yield
  yield
end

def sometimes_block(flag, &block)
  if flag && block
    always_yield &block
  end
end

def sometimes_proc_new(flag)
  if flag && block_given?
    always_yield &Proc.new
  end
end

def sometimes_yield(flag)
  if flag && block_given?
    always_yield { yield }
  end
end

a = b = c = 0
n = 1_000_000
Benchmark.bmbm do |x|
  x.report("no &block") do
    n.times do
      sometimes_block(false) { "won't get used" }
    end
  end
  x.report("no Proc.new") do
    n.times do
      sometimes_proc_new(false) { "won't get used" }
    end
  end
  x.report("no yield") do
    n.times do
      sometimes_yield(false) { "won't get used" }
    end
  end

  x.report("&block") do
    n.times do
      sometimes_block(true) { a += 1 }
    end
  end
  x.report("Proc.new") do
    n.times do
      sometimes_proc_new(true) { b += 1 }
    end
  end
  x.report("yield") do
    n.times do
      sometimes_yield(true) { c += 1 }
    end
  end
end

Performance was similar between Ruby 2.0.0p247 and 1.9.3p392. Here are the results for 1.9.3:

                  user     system      total        real
no &block     0.580000   0.030000   0.610000 (  0.609523)
no Proc.new   0.080000   0.000000   0.080000 (  0.076817)
no yield      0.070000   0.000000   0.070000 (  0.077191)
&block        0.660000   0.030000   0.690000 (  0.689446)
Proc.new      0.820000   0.030000   0.850000 (  0.849887)
yield         0.250000   0.000000   0.250000 (  0.249116)

Adding an explicit &block param when it's not always used really does slow down the method. If the block is optional, do not add it to the method signature. And, for passing blocks around, wrapping yield in another block is fastest.

That said, these are the results for a million iterations, so don't worry about it too much. If one method makes your code clearer at the expense of a millionth of a second, use it anyway.