Module: Diff::LCS

Included in:
Array, String
Defined in:
lib/diff/lcs.rb,
lib/diff/lcs.rb,
lib/diff/lcs/callbacks.rb

Overview

rubocop:disable Style/Documentation

Defined Under Namespace

Modules: Internals, Ldiff Classes: Block, Change, ContextChange, ContextDiffCallbacks, DefaultCallbacks, DiffCallbacks, HTMLDiff, Hunk, SDiffCallbacks

Constant Summary collapse

VERSION =
'1.4.4'
PATCH_MAP =

:nodoc:

{ #:nodoc:
  :patch => { '+' => '+', '-' => '-', '!' => '!', '=' => '=' }.freeze,
  :unpatch => { '+' => '-', '-' => '+', '!' => '!', '=' => '=' }.freeze
}.freeze
SequenceCallbacks =

An alias for DefaultCallbacks that is used in Diff::LCS#traverse_sequences.

Diff::LCS.LCS(seq1, seq2, Diff::LCS::SequenceCallbacks)
DefaultCallbacks
BalancedCallbacks =

An alias for DefaultCallbacks that is used in Diff::LCS#traverse_balanced.

Diff::LCS.LCS(seq1, seq2, Diff::LCS::BalancedCallbacks)
DefaultCallbacks

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.callbacks_for(callbacks) ⇒ Object


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# File 'lib/diff/lcs/callbacks.rb', line 52

def self.callbacks_for(callbacks)
  callbacks.new rescue callbacks
end

.diff(seq1, seq2, callbacks = nil, &block) ⇒ Object

#diff computes the smallest set of additions and deletions necessary to turn the first sequence into the second, and returns a description of these changes.

See Diff::LCS::DiffCallbacks for the default behaviour. An alternate behaviour may be implemented with Diff::LCS::ContextDiffCallbacks. If a Class argument is provided for callbacks, #diff will attempt to initialise it. If the callbacks object (possibly initialised) responds to #finish, it will be called.


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# File 'lib/diff/lcs.rb', line 168

def diff(seq1, seq2, callbacks = nil, &block) # :yields diff changes:
  diff_traversal(:diff, seq1, seq2, callbacks || Diff::LCS::DiffCallbacks, &block)
end

.diff_traversal(method, seq1, seq2, callbacks, &block) ⇒ Object


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# File 'lib/diff/lcs/internals.rb', line 4

def diff_traversal(method, seq1, seq2, callbacks, &block)
  callbacks = callbacks_for(callbacks)
  case method
  when :diff
    traverse_sequences(seq1, seq2, callbacks)
  when :sdiff
    traverse_balanced(seq1, seq2, callbacks)
  end
  callbacks.finish if callbacks.respond_to? :finish

  if block
    callbacks.diffs.map do |hunk|
      if hunk.kind_of? Array
        hunk.map { |hunk_block| block[hunk_block] }
      else
        block[hunk]
      end
    end
  else
    callbacks.diffs
  end
end

.lcs(seq1, seq2, &block) ⇒ Object Also known as: LCS

:yields seq1 for each matched:


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# File 'lib/diff/lcs.rb', line 144

def lcs(seq1, seq2, &block) #:yields seq1[i] for each matched:
  matches = Diff::LCS::Internals.lcs(seq1, seq2)
  ret = []
  string = seq1.kind_of? String
  matches.each_with_index do |_e, i|
    next if matches[i].nil?

    v = string ? seq1[i, 1] : seq1[i]
    v = block[v] if block
    ret << v
  end
  ret
end

.patch(src, patchset, direction = nil) ⇒ Object

Applies a patchset to the sequence src according to the direction (:patch or :unpatch), producing a new sequence.

If the direction is not specified, Diff::LCS::patch will attempt to discover the direction of the patchset.

A patchset can be considered to apply forward (:patch) if the following expression is true:

patch(s1, diff(s1, s2)) -> s2

A patchset can be considered to apply backward (:unpatch) if the following expression is true:

patch(s2, diff(s1, s2)) -> s1

If the patchset contains no changes, the src value will be returned as either src.dup or src. A patchset can be deemed as having no changes if the following predicate returns true:

patchset.empty? or
  patchset.flatten(1).all? { |change| change.unchanged? }

Patchsets

A patchset is always an enumerable sequence of changes, hunks of changes, or a mix of the two. A hunk of changes is an enumerable sequence of changes:

[ # patchset
  # change
  [ # hunk
    # change
  ]
]

The patch method accepts patchsets that are enumerable sequences containing either Diff::LCS::Change objects (or a subclass) or the array representations of those objects. Prior to application, array representations of Diff::LCS::Change objects will be reified.


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# File 'lib/diff/lcs.rb', line 624

def patch(src, patchset, direction = nil)
  # Normalize the patchset.
  has_changes, patchset = Diff::LCS::Internals.analyze_patchset(patchset)

  return src.respond_to?(:dup) ? src.dup : src unless has_changes

  string = src.kind_of?(String)
  # Start with a new empty type of the source's class
  res = src.class.new

  direction ||= Diff::LCS::Internals.intuit_diff_direction(src, patchset)

  ai = bj = 0

  patch_map = PATCH_MAP[direction]

  patchset.each do |change|
    # Both Change and ContextChange support #action
    action = patch_map[change.action]

    case change
    when Diff::LCS::ContextChange
      case direction
      when :patch
        el = change.new_element
        op = change.old_position
        np = change.new_position
      when :unpatch
        el = change.old_element
        op = change.new_position
        np = change.old_position
      end

      case action
      when '-' # Remove details from the old string
        while ai < op
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end
        ai += 1
      when '+'
        while bj < np
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end

        res << el
        bj += 1
      when '='
        # This only appears in sdiff output with the SDiff callback.
        # Therefore, we only need to worry about dealing with a single
        # element.
        res << el

        ai += 1
        bj += 1
      when '!'
        while ai < op
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end

        bj += 1
        ai += 1

        res << el
      end
    when Diff::LCS::Change
      case action
      when '-'
        while ai < change.position
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end
        ai += 1
      when '+'
        while bj < change.position
          res << (string ? src[ai, 1] : src[ai])
          ai += 1
          bj += 1
        end

        bj += 1

        res << change.element
      end
    end
  end

  while ai < src.size
    res << (string ? src[ai, 1] : src[ai])
    ai += 1
    bj += 1
  end

  res
end

.patch!(src, patchset) ⇒ Object

Given a set of patchset, convert the current version to the next version. Does no auto-discovery.


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# File 'lib/diff/lcs.rb', line 734

def patch!(src, patchset)
  patch(src, patchset, :patch)
end

.sdiff(seq1, seq2, callbacks = nil, &block) ⇒ Object

#sdiff computes all necessary components to show two sequences and their minimized differences side by side, just like the Unix utility sdiff does:

old        <     -
same             same
before     |     after
-          >     new

See Diff::LCS::SDiffCallbacks for the default behaviour. An alternate behaviour may be implemented with Diff::LCS::ContextDiffCallbacks. If a Class argument is provided for callbacks, #diff will attempt to initialise it. If the callbacks object (possibly initialised) responds to #finish, it will be called.

Each element of a returned array is a Diff::LCS::ContextChange object, which can be implicitly converted to an array.

Diff::LCS.sdiff(a, b).each do |action, (old_pos, old_element), (new_pos, new_element)|
  case action
  when '!'
    # replace
  when '-'
    # delete
  when '+'
    # insert
  end
end

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# File 'lib/diff/lcs.rb', line 200

def sdiff(seq1, seq2, callbacks = nil, &block) #:yields diff changes:
  diff_traversal(:sdiff, seq1, seq2, callbacks || Diff::LCS::SDiffCallbacks, &block)
end

.traverse_balanced(seq1, seq2, callbacks = Diff::LCS::BalancedCallbacks) ⇒ Object

#traverse_balanced is an alternative to #traverse_sequences. It uses a different algorithm to iterate through the entries in the computed longest common subsequence. Instead of viewing the changes as insertions or deletions from one of the sequences, #traverse_balanced will report changes between the sequences.

The arguments to #traverse_balanced are the two sequences to traverse and a callback object, like this:

traverse_balanced(seq1, seq2, Diff::LCS::ContextDiffCallbacks.new)

#sdiff is implemented with #traverse_balanced.

Callback Methods

Optional callback methods are emphasized.

callbacks#match

Called when a and b are pointing to common elements in A and B.

callbacks#discard_a

Called when a is pointing to an element not in B.

callbacks#discard_b

Called when b is pointing to an element not in A.

callbacks#change

Called when a and b are pointing to the same relative position, but A[a] and B[b] are not the same; a change has occurred.

#traverse_balanced might be a bit slower than #traverse_sequences, noticable only while processing huge amounts of data.

Algorithm

a---+
    v
A = a b c e h j l m n p
B = b c d e f j k l m r s t
    ^
b---+

Matches

If there are two arrows (a and b) pointing to elements of sequences A and B, the arrows will initially point to the first elements of their respective sequences. #traverse_sequences will advance the arrows through the sequences one element at a time, calling a method on the user-specified callback object before each advance. It will advance the arrows in such a way that if there are elements A[i] and B[j] which are both equal and part of the longest common subsequence, there will be some moment during the execution of #traverse_sequences when arrow a is pointing to A[i] and arrow b is pointing to B[j]. When this happens, #traverse_sequences will call callbacks#match and then it will advance both arrows.

Discards

Otherwise, one of the arrows is pointing to an element of its sequence that is not part of the longest common subsequence. #traverse_sequences will advance that arrow and will call callbacks#discard_a or callbacks#discard_b, depending on which arrow it advanced.

Changes

If both a and b point to elements that are not part of the longest common subsequence, then #traverse_sequences will try to call callbacks#change and advance both arrows. If callbacks#change is not implemented, then callbacks#discard_a and callbacks#discard_b will be called in turn.

The methods for callbacks#match, callbacks#discard_a, callbacks#discard_b, and callbacks#change are invoked with an event comprising the action (“=”, “+”, “-”, or “!”, respectively), the indicies i and j, and the elements A[i] and B[j]. Return values are discarded by #traverse_balanced.

Context

Note that i and j may not be the same index position, even if a and b are considered to be pointing to matching or changed elements.


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# File 'lib/diff/lcs.rb', line 475

def traverse_balanced(seq1, seq2, callbacks = Diff::LCS::BalancedCallbacks)
  matches = Diff::LCS::Internals.lcs(seq1, seq2)
  a_size = seq1.size
  b_size = seq2.size
  ai = bj = mb = 0
  ma = -1
  string = seq1.kind_of?(String)

  # Process all the lines in the match vector.
  loop do
    # Find next match indices +ma+ and +mb+
    loop do
      ma += 1
      break unless ma < matches.size and matches[ma].nil?
    end

    break if ma >= matches.size # end of matches?

    mb = matches[ma]

    # Change(seq2)
    while (ai < ma) or (bj < mb)
      ax = string ? seq1[ai, 1] : seq1[ai]
      bx = string ? seq2[bj, 1] : seq2[bj]

      case [(ai < ma), (bj < mb)]
      when [true, true]
        if callbacks.respond_to?(:change)
          event = Diff::LCS::ContextChange.new('!', ai, ax, bj, bx)
          event = yield event if block_given?
          callbacks.change(event)
          ai += 1
        else
          event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx)
          event = yield event if block_given?
          callbacks.discard_a(event)
          ai += 1
          ax = string ? seq1[ai, 1] : seq1[ai]
          event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx)
          event = yield event if block_given?
          callbacks.discard_b(event)
        end

        bj += 1
      when [true, false]
        event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx)
        event = yield event if block_given?
        callbacks.discard_a(event)
        ai += 1
      when [false, true]
        event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx)
        event = yield event if block_given?
        callbacks.discard_b(event)
        bj += 1
      end
    end

    # Match
    ax = string ? seq1[ai, 1] : seq1[ai]
    bx = string ? seq2[bj, 1] : seq2[bj]
    event = Diff::LCS::ContextChange.new('=', ai, ax, bj, bx)
    event = yield event if block_given?
    callbacks.match(event)
    ai += 1
    bj += 1
  end

  while (ai < a_size) or (bj < b_size)
    ax = string ? seq1[ai, 1] : seq1[ai]
    bx = string ? seq2[bj, 1] : seq2[bj]

    case [(ai < a_size), (bj < b_size)]
    when [true, true]
      if callbacks.respond_to?(:change)
        event = Diff::LCS::ContextChange.new('!', ai, ax, bj, bx)
        event = yield event if block_given?
        callbacks.change(event)
        ai += 1
      else
        event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx)
        event = yield event if block_given?
        callbacks.discard_a(event)
        ai += 1
        ax = string ? seq1[ai, 1] : seq1[ai]
        event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx)
        event = yield event if block_given?
        callbacks.discard_b(event)
      end

      bj += 1
    when [true, false]
      event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx)
      event = yield event if block_given?
      callbacks.discard_a(event)
      ai += 1
    when [false, true]
      event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx)
      event = yield event if block_given?
      callbacks.discard_b(event)
      bj += 1
    end
  end
end

.traverse_sequences(seq1, seq2, callbacks = Diff::LCS::SequenceCallbacks) ⇒ Object

#traverse_sequences is the most general facility provided by this module; #diff and #lcs are implemented as calls to it.

The arguments to #traverse_sequences are the two sequences to traverse, and a callback object, like this:

traverse_sequences(seq1, seq2, Diff::LCS::ContextDiffCallbacks.new)

Callback Methods

Optional callback methods are emphasized.

callbacks#match

Called when a and b are pointing to common elements in A and B.

callbacks#discard_a

Called when a is pointing to an element not in B.

callbacks#discard_b

Called when b is pointing to an element not in A.

callbacks#finished_a

Called when a has reached the end of sequence A.

callbacks#finished_b

Called when b has reached the end of sequence B.

Algorithm

a---+
    v
A = a b c e h j l m n p
B = b c d e f j k l m r s t
    ^
b---+

If there are two arrows (a and b) pointing to elements of sequences A and B, the arrows will initially point to the first elements of their respective sequences. #traverse_sequences will advance the arrows through the sequences one element at a time, calling a method on the user-specified callback object before each advance. It will advance the arrows in such a way that if there are elements A[i] and B[j] which are both equal and part of the longest common subsequence, there will be some moment during the execution of #traverse_sequences when arrow a is pointing to A[i] and arrow b is pointing to B[j]. When this happens, #traverse_sequences will call callbacks#match and then it will advance both arrows.

Otherwise, one of the arrows is pointing to an element of its sequence that is not part of the longest common subsequence. #traverse_sequences will advance that arrow and will call callbacks#discard_a or callbacks#discard_b, depending on which arrow it advanced. If both arrows point to elements that are not part of the longest common subsequence, then #traverse_sequences will advance one of them and call the appropriate callback, but it is not specified which it will call.

The methods for callbacks#match, callbacks#discard_a, and callbacks#discard_b are invoked with an event comprising the action (“=”, “+”, or “-”, respectively), the indicies i and j, and the elements A[i] and B[j]. Return values are discarded by #traverse_sequences.

End of Sequences

If arrow a reaches the end of its sequence before arrow b does, #traverse_sequence will try to call callbacks#finished_a with the last index and element of A (A[-1]) and the current index and element of B (B[j]). If callbacks#finished_a does not exist, then callbacks#discard_b will be called on each element of B until the end of the sequence is reached (the call will be done with A[-1] and B[j] for each element).

If b reaches the end of B before a reaches the end of A, callbacks#finished_b will be called with the current index and element of A (A[i]) and the last index and element of B (A[-1]). Again, if callbacks#finished_b does not exist on the callback object, then callbacks#discard_a will be called on each element of A until the end of the sequence is reached (A[i] and B[-1]).

There is a chance that one additional callbacks#discard_a or callbacks#discard_b will be called after the end of the sequence is reached, if a has not yet reached the end of A or b has not yet reached the end of B.


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# File 'lib/diff/lcs.rb', line 284

def traverse_sequences(seq1, seq2, callbacks = Diff::LCS::SequenceCallbacks) #:yields change events:
  callbacks ||= Diff::LCS::SequenceCallbacks
  matches = Diff::LCS::Internals.lcs(seq1, seq2)

  run_finished_a = run_finished_b = false
  string = seq1.kind_of?(String)

  a_size = seq1.size
  b_size = seq2.size
  ai = bj = 0

  (0..matches.size).each do |i|
    b_line = matches[i]

    ax = string ? seq1[i, 1] : seq1[i]
    bx = string ? seq2[bj, 1] : seq2[bj]

    if b_line.nil?
      unless ax.nil? or (string and ax.empty?)
        event = Diff::LCS::ContextChange.new('-', i, ax, bj, bx)
        event = yield event if block_given?
        callbacks.discard_a(event)
      end
    else
      loop do
        break unless bj < b_line

        bx = string ? seq2[bj, 1] : seq2[bj]
        event = Diff::LCS::ContextChange.new('+', i, ax, bj, bx)
        event = yield event if block_given?
        callbacks.discard_b(event)
        bj += 1
      end
      bx = string ? seq2[bj, 1] : seq2[bj]
      event = Diff::LCS::ContextChange.new('=', i, ax, bj, bx)
      event = yield event if block_given?
      callbacks.match(event)
      bj += 1
    end
    ai = i
  end
  ai += 1

  # The last entry (if any) processed was a match. +ai+ and +bj+ point just
  # past the last matching lines in their sequences.
  while (ai < a_size) or (bj < b_size)
    # last A?
    if ai == a_size and bj < b_size
      if callbacks.respond_to?(:finished_a) and !run_finished_a
        ax = string ? seq1[-1, 1] : seq1[-1]
        bx = string ? seq2[bj, 1] : seq2[bj]
        event = Diff::LCS::ContextChange.new('>', (a_size - 1), ax, bj, bx)
        event = yield event if block_given?
        callbacks.finished_a(event)
        run_finished_a = true
      else
        ax = string ? seq1[ai, 1] : seq1[ai]
        loop do
          bx = string ? seq2[bj, 1] : seq2[bj]
          event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx)
          event = yield event if block_given?
          callbacks.discard_b(event)
          bj += 1
          break unless bj < b_size
        end
      end
    end

    # last B?
    if bj == b_size and ai < a_size
      if callbacks.respond_to?(:finished_b) and !run_finished_b
        ax = string ? seq1[ai, 1] : seq1[ai]
        bx = string ? seq2[-1, 1] : seq2[-1]
        event = Diff::LCS::ContextChange.new('<', ai, ax, (b_size - 1), bx)
        event = yield event if block_given?
        callbacks.finished_b(event)
        run_finished_b = true
      else
        bx = string ? seq2[bj, 1] : seq2[bj]
        loop do
          ax = string ? seq1[ai, 1] : seq1[ai]
          event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx)
          event = yield event if block_given?
          callbacks.discard_a(event)
          ai += 1
          break unless bj < b_size
        end
      end
    end

    if ai < a_size
      ax = string ? seq1[ai, 1] : seq1[ai]
      bx = string ? seq2[bj, 1] : seq2[bj]
      event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx)
      event = yield event if block_given?
      callbacks.discard_a(event)
      ai += 1
    end

    next unless bj < b_size

    ax = string ? seq1[ai, 1] : seq1[ai]
    bx = string ? seq2[bj, 1] : seq2[bj]
    event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx)
    event = yield event if block_given?
    callbacks.discard_b(event)
    bj += 1
  end
end

.unpatch!(src, patchset) ⇒ Object

Given a set of patchset, convert the current version to the prior version. Does no auto-discovery.


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# File 'lib/diff/lcs.rb', line 728

def unpatch!(src, patchset)
  patch(src, patchset, :unpatch)
end

Instance Method Details

#diff(other, callbacks = nil, &block) ⇒ Object

Returns the difference set between self and other. See Diff::LCS#diff.


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# File 'lib/diff/lcs.rb', line 75

def diff(other, callbacks = nil, &block)
  Diff::LCS.diff(self, other, callbacks, &block)
end

#lcs(other, &block) ⇒ Object

Returns an Array containing the longest common subsequence(s) between self and other. See Diff::LCS#lcs.

lcs = seq1.lcs(seq2)

A note when using objects: Diff::LCS only works properly when each object can be used as a key in a Hash, which typically means that the objects must implement Object#eql? in a way that two identical values compare identically for key purposes. That is:

O.new('a').eql?(O.new('a')) == true

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# File 'lib/diff/lcs.rb', line 70

def lcs(other, &block) #:yields self[i] if there are matched subsequences:
  Diff::LCS.lcs(self, other, &block)
end

#patch(patchset) ⇒ Object

Attempts to patch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#patch. Attempts to autodiscover the direction of the patch.


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# File 'lib/diff/lcs.rb', line 101

def patch(patchset)
  Diff::LCS.patch(self, patchset)
end

#patch!(patchset) ⇒ Object

Attempts to patch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#patch. Does no patch direction autodiscovery.


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# File 'lib/diff/lcs.rb', line 109

def patch!(patchset)
  Diff::LCS.patch!(self, patchset)
end

#patch_me(patchset) ⇒ Object

Attempts to patch self with the provided patchset, using #patch!. If the sequence this is used on supports #replace, the value of self will be replaced. See Diff::LCS#patch. Does no patch direction autodiscovery.


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# File 'lib/diff/lcs.rb', line 123

def patch_me(patchset)
  if respond_to? :replace
    replace(patch!(patchset))
  else
    patch!(patchset)
  end
end

#sdiff(other, callbacks = nil, &block) ⇒ Object

Returns the balanced (“side-by-side”) difference set between self and other. See Diff::LCS#sdiff.


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# File 'lib/diff/lcs.rb', line 81

def sdiff(other, callbacks = nil, &block)
  Diff::LCS.sdiff(self, other, callbacks, &block)
end

#traverse_balanced(other, callbacks = nil, &block) ⇒ Object

Traverses the discovered longest common subsequences between self and other using the alternate, balanced algorithm. See Diff::LCS#traverse_balanced.


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# File 'lib/diff/lcs.rb', line 94

def traverse_balanced(other, callbacks = nil, &block)
  traverse_balanced(self, other, callbacks || Diff::LCS::BalancedCallbacks, &block)
end

#traverse_sequences(other, callbacks = nil, &block) ⇒ Object

Traverses the discovered longest common subsequences between self and other. See Diff::LCS#traverse_sequences.


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# File 'lib/diff/lcs.rb', line 87

def traverse_sequences(other, callbacks = nil, &block)
  traverse_sequences(self, other, callbacks || Diff::LCS::SequenceCallbacks, &block)
end

#unpatchObject

Attempts to patch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#patch. Attempts to autodiscover the direction of the patch.


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# File 'lib/diff/lcs.rb', line 104

def patch(patchset)
  Diff::LCS.patch(self, patchset)
end

#unpatch!(patchset) ⇒ Object

Attempts to unpatch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#unpatch. Does no patch direction autodiscovery.


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# File 'lib/diff/lcs.rb', line 116

def unpatch!(patchset)
  Diff::LCS.unpatch!(self, patchset)
end

#unpatch_me(patchset) ⇒ Object

Attempts to unpatch self with the provided patchset, using #unpatch!. If the sequence this is used on supports #replace, the value of self will be replaced. See Diff::LCS#unpatch. Does no patch direction autodiscovery.


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# File 'lib/diff/lcs.rb', line 134

def unpatch_me(patchset)
  if respond_to? :replace
    replace(unpatch!(patchset))
  else
    unpatch!(patchset)
  end
end