unindent.rb

TEXT = <<EOF
   See, the interesting thing about this text
     is that while it seems like the first line defines an indent
       it's actually the last line which has the smallest indent

    there are also some blank lines

    both with and without extra spaces in them

    and it just goes on and on

       this text

    and starts to repeat itself
   See, the interesting thing about this text
     is that while it seems like the first line defines an indent
       it's actually the last line which has the smallest indent

    there are also some blank lines

    both with and without extra spaces in them

    and it just goes on and on

       this text

    and starts to repeat itself
   See, the interesting thing about this text
     is that while it seems like the first line defines an indent
       it's actually the last line which has the smallest indent

    there are also some blank lines

    both with and without extra spaces in them

    and it just goes on and on

       this text

    and starts to repeat itself

  The End.
EOF

EXPECTED_TEXT = <<EOF
 See, the interesting thing about this text
   is that while it seems like the first line defines an indent
     it's actually the last line which has the smallest indent

  there are also some blank lines

  both with and without extra spaces in them

  and it just goes on and on

     this text

  and starts to repeat itself
 See, the interesting thing about this text
   is that while it seems like the first line defines an indent
     it's actually the last line which has the smallest indent

  there are also some blank lines

  both with and without extra spaces in them

  and it just goes on and on

     this text

  and starts to repeat itself
 See, the interesting thing about this text
   is that while it seems like the first line defines an indent
     it's actually the last line which has the smallest indent

  there are also some blank lines

  both with and without extra spaces in them

  and it just goes on and on

     this text

  and starts to repeat itself

The End.
EOF

require 'active_support/core_ext/string'
require 'minitest/autorun'
require 'minitest/pride'
require 'unindent'

class String

  # Try to optimize by avoiding splitting into an array
  def unindent_scan
    indent_str = nil
    scan(/^[\t ]*(?=\S)/) do |s|
      indent_str ||= s
      indent_str = (s.size < indent_str.size) ? s : indent_str
    end
    if indent_str
      gsub(/^#{indent_str}/, "")
    end
  end

  # This version tries to avoid a second traversal of the string by
  # saving a list of offsets. However, it winds up being
  # slower. Perhaps this is a sign of how well-optimized #gsub is?
  def unindent_offsets
    min_indent = nil
    offsets    = []
    scan(/^[\t ]*(?=\S)/) do |s|
      offsets << $~.offset(0).first
      min_indent ||= s.size
      min_indent = (s.size < min_indent.size) ? s.size : min_indent
    end
    if min_indent
      result = dup
      shift  = 0
      offsets.each do |offset|
        result[offset - shift, min_indent] = ""
        shift += min_indent
      end
      result
    else
      self
    end
  end

  def unindent_by_min_dent
    dent = split("\n").reject(&:empty?).map { |line| line[/^\s*/] }.min_by(&:size)
    gsub(/^#{dent}/, '')
  end
end

class TestUnindent < MiniTest::Test
  def test_unindent_gem
    assert_equal EXPECTED_TEXT, TEXT.unindent
  end

  def test_activesupport
    assert_equal EXPECTED_TEXT, TEXT.strip_heredoc
  end

  def test_scan
    assert_equal EXPECTED_TEXT, TEXT.unindent_scan
  end

  def test_offsets
    assert_equal EXPECTED_TEXT, TEXT.unindent_offsets
  end

  def test_by_min_dent
    assert_equal EXPECTED_TEXT, TEXT.unindent_by_min_dent
  end
end

require 'benchmark/ips'

Benchmark.ips do |x|
  x.report('unindent gem')  { TEXT.unindent             }
  x.report('activesupport') { TEXT.strip_heredoc        }
  x.report('scan')          { TEXT.unindent_scan        }
  x.report('offsets')       { TEXT.unindent_offsets     }
  x.report('min dent')      { TEXT.unindent_by_min_dent }
end

# Calculating -------------------------------------
#         unindent gem      1041 i/100ms
#        activesupport      1319 i/100ms
#                 scan      1605 i/100ms
#              offsets      1157 i/100ms
#             min dent      1892 i/100ms
# -------------------------------------------------
#         unindent gem    11316.3 (±0.7%) i/s -      57255 in   5.059733s
#        activesupport    14493.9 (±0.6%) i/s -      72545 in   5.005421s
#                 scan    17936.8 (±0.7%) i/s -      89880 in   5.011144s
#              offsets    12385.2 (±1.3%) i/s -      62478 in   5.045426s
#             min dent    21625.3 (±1.1%) i/s -     109736 in   5.075009s
# Run options: --seed 1239
#
# # Running:
#
# .....
#
# Fabulous run in 0.001733s, 2885.9696 runs/s, 2885.9696 assertions/s.
#
# 5 runs, 5 assertions, 0 failures, 0 errors, 0 skips

Please gem install activesupport benchmark-ips minitest unindent before running this.

Numbers for MRI 2.1.2 (from ruby-install + chruby) on x86_64-linux – Ubuntu 14.04 on i7-3517U.

Hat tip to the great @sferik for introducing me to benchmark-ips in his Writing Fast Ruby talk.

And now there’s this: https://gist.github.com/danielfone/eacaf4a1f1d7f2ad425f :)