NAME
    Data::Cmp - Compare two data structures, return -1/0/1 like cmp

VERSION
    This document describes version 0.005 of Data::Cmp (from Perl
    distribution Data-Cmp), released on 2018-08-13.

SYNOPSIS
     use Data::Cmp qw(cmp_data);

     cmp_data(["one", "two", "three"],
              ["one", "two", "three"]); # => 0

     cmp_data(["one", "two" , "three"],
              ["one", "two2", "three"]); # => -1

     cmp_data(["one", "two", "three"],
              ["one", "TWO", "three"]); # => 1

     # hash/array is not "comparable" with scalar
     cmp_data(["one", "two", {}],
              ["one", "two", "three"]); # => 2

    Sort data structures (of similar structures):

     my @arrays = (["c"], ["b"], ["a", "b"], ["a"], ["a","c"]);
     my @sorted = sort { cmp_data($a, $b) } @arrays; # => (["a"], ["a","b"], ["a","c"], ["b"], ["c"])

DESCRIPTION
    This relatively lightweight (no non-core dependencies, under 100 lines
    of code) module offers the "cmp_data" function that, like Perl's "cmp",
    returns -1/0/1 value. In addition to that, it can also return 2 if the
    two data structures differ but there is no sensible notion of which one
    is "greater than" the other.

    This module can handle circular structure.

    The following are the rules of comparison used by "cmp_data()":

    *   Two undefs are the same

         cmp_data(undef, undef); # 0

    *   A defined value is greater than undef

         cmp_data(undef, 0); # -1

    *   Two non-reference scalars are compared string-wise using Perl's cmp

         cmp_data("a", "A"); # 1
         cmp_data(10, 9);    # -1

    *   A reference and non-reference are different

         cmp_data([], 0); # 2

    *   Two references that are of different types are different

         cmp_data([], {}); # 2

    *   Blessed references that are blessed into different packages are
        different

         cmp_data(bless([], "foo"), bless([], "bar")); # 2
         cmp_data(bless([], "foo"), bless([], "foo")); # 0

    *   Two array references are compared element by element (unless an
        array has been seen, see last rule)

         cmp_data(["a","b","c"], ["a","b","c"]); #  0
         cmp_data(["a","b","c"], ["a","b","d"]); # -1
         cmp_data(["a","d","c"], ["a","b","e"]); #  1

    *   A longer arrayref is greater than its shorter subset

         cmp_data(["a","b"], ["a"]); # 1

    *   Two hash references are compared key by key (unless an array has
        been seen, see last rule)

         cmp_data({k1=>"a", k2=>"b", k3=>"c"}, {k1=>"a", k2=>"b", k3=>"d"}); # 0
         cmp_data({k1=>"a", k2=>"b", k3=>"c"}, {k1=>"a", k2=>"b", k3=>"c"}); # 1

    *   When two hash references share a common subset of pairs but have
        non-common pairs, the greater hashref is the one that has more
        non-common pairs

        If the number of non-common pairs are the same, they are just
        different.

         cmp_data({k1=>"", k2=>"", k3=>""}, {k1=>"", k5=>""});                #  1
         cmp_data({k1=>"", k2=>"", k3=>""}, {k1=>"", k5=>"", k6=>"});         #  2
         cmp_data({k1=>"", k2=>"", k3=>""}, {k1=>"", k5=>"", k6=>", k7=>""}); # -1

    *   All other types of references (i.e. non-hash, non-array) are the
        same only if their address is

         cmp_data(\1, \1); # 2
         my $ref = \1; cmp_data($ref, $ref); # 0

    *   A seen (hash or array) reference is no longer recursed, it's
        compared by address (see previous rule)

         my $ary1 = [1]; push @$ary1, $ary1;
         my $ary2 = [1]; push @$ary2, $ary2;
         my $ary3 = [1]; push @$ary3, $ary1;
         cmp_data($ary1, $ary2); # 1
         cmp_data($ary1, $ary3); # 0

FUNCTIONS
  cmp_data
    Usage:

     cmp_data($d1, $d2) => -1/0/1/2

HOMEPAGE
    Please visit the project's homepage at
    <https://metacpan.org/release/Data-Cmp>.

SOURCE
    Source repository is at <https://github.com/perlancar/perl-Data-Cmp>.

BUGS
    Please report any bugs or feature requests on the bugtracker website
    <https://rt.cpan.org/Public/Dist/Display.html?Name=Data-Cmp>

    When submitting a bug or request, please include a test-file or a patch
    to an existing test-file that illustrates the bug or desired feature.

SEE ALSO
    Other variants of Data::Cmp: Data::Cmp::Numeric,
    Data::Cmp::StrOrNumeric, Data::Cmp::Custom (allows custom actions and
    comparison routines), Data::Cmp::Diff (generates diff structure instead
    of just returning -1/0/1/2), Data::Cmp::Diff::Perl (generates diff in
    the form of Perl code).

    Modules that just return boolean result ("same or different"):
    Data::Compare, Test::Deep::NoTest (offers flexibility or approximate or
    custom comparison).

    Modules that return some kind of "diff" data: Data::Comparator,
    Data::Diff.

    Of course, to check whether two structures are the same you can also
    serialize each one then compare the serialized strings/bytes. There are
    many modules for serialization: JSON, YAML, Sereal, Data::Dumper,
    Storable, Data::Dmp, just to name a few.

    Test modules that do data structure comparison: Test::DataCmp (test
    module based on Data::Cmp::Custom), Test::More ("is_deeply()"),
    Test::Deep, Test2::Tools::Compare.

AUTHOR
    perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE
    This software is copyright (c) 2018 by perlancar@cpan.org.

    This is free software; you can redistribute it and/or modify it under
    the same terms as the Perl 5 programming language system itself.

