regexp_interpolation.rb

require 'benchmark'
var = "a_string"
TIMES = 1_000_000

Benchmark.bmbm do |x|
  x.report("//") do
    TIMES.times { /a#{var}b/ }
  end

  # note: this regexp will only be built once for all iterations
  x.report("//o") do
    TIMES.times { /#{var}/o }
  end

  x.report("Regexp.new") do
    TIMES.times { Regexp.new("a#{var}b") }
  end
end

# Rehearsal ----------------------------------------------
# //          14.470000   0.020000  14.490000 ( 14.616450)
# //o          0.170000   0.000000   0.170000 (  0.176770)
# Regexp.new  10.080000   0.020000  10.100000 ( 10.074714)
# ------------------------------------ total: 24.760000sec

#                  user     system      total        real
# //          13.670000   0.020000  13.690000 ( 13.710231)
# //o          0.180000   0.000000   0.180000 (  0.177539)
# Regexp.new  10.080000   0.020000  10.100000 ( 10.117770)