= Diff::LCS

home :: https://github.com/halostatue/diff-lcs
code :: https://github.com/halostatue/diff-lcs
bugs :: https://github.com/halostatue/diff-lcs/issues
rdoc :: http://rubydoc.info/github/halostatue/diff-lcs
continuous integration :: {<img src="https://travis-ci.org/halostatue/diff-lcs.svg" />}[https://travis-ci.org/halostatue/diff-lcs]
test coverage :: {<img src="https://coveralls.io/repos/halostatue/diff-lcs/badge.svg" alt="Coverage Status" />}[https://coveralls.io/r/halostatue/diff-lcs]

== Description

Diff::LCS computes the difference between two Enumerable sequences using the
McIlroy-Hunt longest common subsequence (LCS) algorithm. It includes utilities
to create a simple HTML diff output format and a standard diff-like tool.

This is release 1.4, providing a simple extension that allows for
Diff::LCS::Change objects to be treated implicitly as arrays. Ruby versions
below 2.3 are soft-deprecated.

This means that older versions are no longer part of the CI test suite. If any
changes have been introduced that break those versions, bug reports and patches
will be accepted, but it will be up to the reporter to verify any fixes prior
to release. A future release will completely break compatibility.

== Synopsis

Using this module is quite simple. By default, Diff::LCS does not extend
objects with the Diff::LCS interface, but will be called as if it were a
function:

  require 'diff/lcs'

  seq1 = %w(a b c e h j l m n p)
  seq2 = %w(b c d e f j k l m r s t)

  lcs = Diff::LCS.LCS(seq1, seq2)
  diffs = Diff::LCS.diff(seq1, seq2)
  sdiff = Diff::LCS.sdiff(seq1, seq2)
  seq = Diff::LCS.traverse_sequences(seq1, seq2, callback_obj)
  bal = Diff::LCS.traverse_balanced(seq1, seq2, callback_obj)
  seq2 == Diff::LCS.patch!(seq1, diffs)
  seq1 == Diff::LCS.unpatch!(seq2, diffs)
  seq2 == Diff::LCS.patch!(seq1, sdiff)
  seq1 == Diff::LCS.unpatch!(seq2, sdiff)

Objects can be extended with Diff::LCS:

  seq1.extend(Diff::LCS)
  lcs = seq1.lcs(seq2)
  diffs = seq1.diff(seq2)
  sdiff = seq1.sdiff(seq2)
  seq = seq1.traverse_sequences(seq2, callback_obj)
  bal = seq1.traverse_balanced(seq2, callback_obj)
  seq2 == seq1.patch!(diffs)
  seq1 == seq2.unpatch!(diffs)
  seq2 == seq1.patch!(sdiff)
  seq1 == seq2.unpatch!(sdiff)

By requiring 'diff/lcs/array' or 'diff/lcs/string', Array or String will be
extended for use this way.

Note that Diff::LCS requires a sequenced enumerable container, which means that
the order of enumeration is both predictable and consistent for the same set of
data. While it is theoretically possible to generate a diff for an unordered
hash, it will only be meaningful if the enumeration of the hashes is
consistent. In general, this will mean that containers that behave like String
or Array will perform best.

== History

Diff::LCS is a port of Perl's Algorithm::Diff that uses the McIlroy-Hunt
longest common subsequence (LCS) algorithm to compute intelligent differences
between two sequenced enumerable containers. The implementation is based on
Mario I. Wolczko's
{Smalltalk version 1.2}[ftp://st.cs.uiuc.edu/pub/Smalltalk/MANCHESTER/manchester/4.0/diff.st]
(1993) and Ned Konz's Perl version
{Algorithm::Diff 1.15}[http://search.cpan.org/~nedkonz/Algorithm-Diff-1.15/].
Diff::LCS#sdiff and Diff::LCS#traverse_balanced were originally written for the
Perl version by Mike Schilli.

The algorithm is described in <em>A Fast Algorithm for Computing Longest Common
Subsequences</em>, CACM, vol.20, no.5, pp.350-353, May 1977, with a few minor
improvements to improve the speed. A simplified description of the algorithm,
originally written for the Perl version, was written by Mark-Jason Dominus.