Algorithm::DiffOld(3)

🌸 NAME 🌸

Okay bestie, welcome to Algorithm::DiffOld — the page from the User Contributed Perl Documentation known as Algorithm::DiffOld(3). It computes intelligent differences between two files / lists but use the old (<=0.59) interface. Old-school era, but make it diff.

🚨 NOTE 🚨

This has been provided as part of the Algorithm::Diff package by Ned Konz. This particular module is ONLY for people who HAVE to have the old interface, which uses a comparison function rather than a key generating function.

🫶 Real talk: this is for the “I literally must use the old interface” girlies. It is not the sparkly low-effort path.

Because each of the lines in one array have to be compared with each of the lines in the other array, this does M*N comparisons. This can be very slow. Ned clocked it at taking 18 times as long as the stock version of Algorithm::Diff for a 4000-line file. It will get worse quadratically as array sizes increase. 😭

✨ SYNOPSIS ✨

Here’s the vibe in code, bestie:

  use Algorithm::DiffOld qw(diff LCS traverse_sequences);

  @lcs    = LCS( \@seq1, \@seq2, $comparison_function );

  $lcsref = LCS( \@seq1, \@seq2, $comparison_function );

  @diffs = diff( \@seq1, \@seq2, $comparison_function );

  traverse_sequences( \@seq1, \@seq2,
                     { MATCH => $callback,
                       DISCARD_A => $callback,
                       DISCARD_B => $callback,
                     },
                     $comparison_function );

💅 COMPARISON FUNCTIONS 💅

Each of the main routines should be passed a comparison function. If you aren’t passing one in, use Algorithm::Diff instead. No cap.

These functions should return a true value when two items should compare as equal.

For instance:

  @lcs    = LCS( \@seq1, \@seq2, sub { my ($a, $b) = @_; $a eq $b } );

but if that is all you’re doing with your comparison function, just use Algorithm::Diff and let it do this (this is its default). Slay, less work.

Or:

  sub someFunkyComparisonFunction
  {
        my ($a, $b) = @_;
        $a =~ m{$b};
  }

  @diffs = diff( \@lines, \@patterns, \&someFunkyComparisonFunction );

which would allow you to diff an array @lines which consists of text lines with an array @patterns which consists of regular expressions. Regex-to-lines matching? Iconic.

This is actually the reason Ned wrote this version -- there is no way to do this with a key generation function as in the stock Algorithm::Diff. Main character author moment.

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That’s the whole page, bestie. This one’s from perl v5.32.1, dated 2021-08-09, and it’s literally Algorithm::DiffOld(3). Stay diffy, and hydrate before you compare every line to every other line 💖💅