Provided by: libhash-merge-perl_0.200-1_all 
NAME
Hash::Merge - Merges arbitrarily deep hashes into a single hash
SYNOPSIS
use Hash::Merge qw( merge );
my %a = (
'foo' => 1,
'bar' => [ qw( a b e ) ],
'querty' => { 'bob' => 'alice' },
);
my %b = (
'foo' => 2,
'bar' => [ qw(c d) ],
'querty' => { 'ted' => 'margeret' },
);
my %c = %{ merge( \%a, \%b ) };
Hash::Merge::set_behavior( 'RIGHT_PRECEDENT' );
# This is the same as above
Hash::Merge::specify_behavior(
{
'SCALAR' => {
'SCALAR' => sub { $_[1] },
'ARRAY' => sub { [ $_[0], @{$_[1]} ] },
'HASH' => sub { $_[1] },
},
'ARRAY => {
'SCALAR' => sub { $_[1] },
'ARRAY' => sub { [ @{$_[0]}, @{$_[1]} ] },
'HASH' => sub { $_[1] },
},
'HASH' => {
'SCALAR' => sub { $_[1] },
'ARRAY' => sub { [ values %{$_[0]}, @{$_[1]} ] },
'HASH' => sub { Hash::Merge::_merge_hashes( $_[0], $_[1] ) },
},
},
'My Behavior',
);
# Also there is OO interface.
my $merge = Hash::Merge->new( 'LEFT_PRECEDENT' );
my %c = %{ $merge->merge( \%a, \%b ) };
# All behavioral changes (e.g. $merge->set_behavior(...)), called on an object remain specific to that object
# The legacy "Global Setting" behavior is respected only when new called as a non-OO function.
DESCRIPTION
Hash::Merge merges two arbitrarily deep hashes into a single hash. That is, at any level, it will add
non-conflicting key-value pairs from one hash to the other, and follows a set of specific rules when
there are key value conflicts (as outlined below). The hash is followed recursively, so that deeply
nested hashes that are at the same level will be merged when the parent hashes are merged. Please note
that self-referencing hashes, or recursive references, are not handled well by this method.
Values in hashes are considered to be either ARRAY references, HASH references, or otherwise are treated
as SCALARs. By default, the data passed to the merge function will be cloned using the Clone module;
however, if necessary, this behavior can be changed to use as many of the original values as possible.
(See "set_clone_behavior").
Because there are a number of possible ways that one may want to merge values when keys are conflicting,
Hash::Merge provides several preset methods for your convenience, as well as a way to define you own.
These are (currently):
Left Precedence
This is the default behavior.
The values buried in the left hash will never be lost; any values that can be added from the right
hash will be attempted.
my $merge = Hash::Merge->new();
my $merge = Hash::Merge->new('LEFT_PRECEDENT');
$merge->set_set_behavior('LEFT_PRECEDENT')
Hash::Merge::set_set_behavior('LEFT_PRECEDENT')
Right Precedence
Same as Left Precedence, but with the right hash values never being lost
my $merge = Hash::Merge->new('RIGHT_PRECEDENT');
$merge->set_set_behavior('RIGHT_PRECEDENT')
Hash::Merge::set_set_behavior('RIGHT_PRECEDENT')
Storage Precedence
If conflicting keys have two different storage mediums, the 'bigger' medium will win; arrays are
preferred over scalars, hashes over either. The other medium will try to be fitted in the other, but
if this isn't possible, the data is dropped.
my $merge = Hash::Merge->new('STORAGE_PRECEDENT');
$merge->set_set_behavior('STORAGE_PRECEDENT')
Hash::Merge::set_set_behavior('STORAGE_PRECEDENT')
Retainment Precedence
No data will be lost; scalars will be joined with arrays, and scalars and arrays will be 'hashified'
to fit them into a hash.
my $merge = Hash::Merge->new('RETAINMENT_PRECEDENT');
$merge->set_set_behavior('RETAINMENT_PRECEDENT')
Hash::Merge::set_set_behavior('RETAINMENT_PRECEDENT')
Specific descriptions of how these work are detailed below.
merge ( <hashref>, <hashref> )
Merges two hashes given the rules specified. Returns a reference to the new hash.
_hashify( <scalar>|<arrayref> ) -- INTERNAL FUNCTION
Returns a reference to a hash created from the scalar or array reference, where, for the scalar
value, or each item in the array, there is a key and it's value equal to that specific value.
Example, if you pass scalar '3', the hash will be { 3 => 3 }.
_merge_hashes( <hashref>, <hashref> ) -- INTERNAL FUNCTION
Actually does the key-by-key evaluation of two hashes and returns the new merged hash. Note that
this recursively calls "merge".
set_clone_behavior( <scalar> )
Sets how the data cloning is handled by Hash::Merge. If this is true, then data will be cloned; if
false, then original data will be used whenever possible. By default, cloning is on (set to true).
get_clone_behavior( )
Returns the current behavior for data cloning.
set_behavior( <scalar> )
Specify which built-in behavior for merging that is desired. The scalar must be one of those given
below.
get_behavior( )
Returns the behavior that is currently in use by Hash::Merge.
specify_behavior( <hashref>, [<name>] )
Specify a custom merge behavior for Hash::Merge. This must be a hashref defined with (at least) 3
keys, SCALAR, ARRAY, and HASH; each of those keys must have another hashref with (at least) the same
3 keys defined. Furthermore, the values in those hashes must be coderefs. These will be called with
two arguments, the left and right values for the merge. Your coderef should return either a scalar
or an array or hash reference as per your planned behavior. If necessary, use the functions _hashify
and _merge_hashes as helper functions for these. For example, if you want to add the left SCALAR to
the right ARRAY, you can have your behavior specification include:
%spec = ( ...SCALAR => { ARRAY => sub { [ $_[0], @$_[1] ] }, ... } } );
Note that you can import _hashify and _merge_hashes into your program's namespace with the 'custom'
tag.
BUILT-IN BEHAVIORS
Here is the specifics on how the current internal behaviors are called, and what each does. Assume that
the left value is given as $a, and the right as $b (these are either scalars or appropriate references)
LEFT TYPE RIGHT TYPE LEFT_PRECEDENT RIGHT_PRECEDENT
SCALAR SCALAR $a $b
SCALAR ARRAY $a ( $a, @$b )
SCALAR HASH $a %$b
ARRAY SCALAR ( @$a, $b ) $b
ARRAY ARRAY ( @$a, @$b ) ( @$a, @$b )
ARRAY HASH ( @$a, values %$b ) %$b
HASH SCALAR %$a $b
HASH ARRAY %$a ( values %$a, @$b )
HASH HASH merge( %$a, %$b ) merge( %$a, %$b )
LEFT TYPE RIGHT TYPE STORAGE_PRECEDENT RETAINMENT_PRECEDENT
SCALAR SCALAR $a ( $a ,$b )
SCALAR ARRAY ( $a, @$b ) ( $a, @$b )
SCALAR HASH %$b merge( hashify( $a ), %$b )
ARRAY SCALAR ( @$a, $b ) ( @$a, $b )
ARRAY ARRAY ( @$a, @$b ) ( @$a, @$b )
ARRAY HASH %$b merge( hashify( @$a ), %$b )
HASH SCALAR %$a merge( %$a, hashify( $b ) )
HASH ARRAY %$a merge( %$a, hashify( @$b ) )
HASH HASH merge( %$a, %$b ) merge( %$a, %$b )
(*) note that merge calls _merge_hashes, hashify calls _hashify.
CAVEATS
This will not handle self-referencing/recursion within hashes well. Plans for a future version include
incorporate deep recursion protection.
As of Feb 16, 2002, ActiveState Perl's PPM of Clone.pm is only at 0.09. This version does not support
the cloning of scalars if passed to the function. This is fixed by 0.10 (and currently, Clone.pm is at
0.13). So while most other users can upgrade their Clone.pm appropriately (and I could put this as a
requirement into the Makefile.PL), those using ActiveState would lose out on the ability to use this
module. (Clone.pm is not pure perl, so it's not simply a matter of moving the newer file into place).
Thus, for the time being, a check is done at the start of loading of this module to see if a newer
version of clone is around. Then, all cloning calls have been wrapped in the internal _my_clone function
to block any scalar clones if Clone.pm is too old. However, this also prevents the cloning of anything
that isn't a hash or array under the same conditions. Once ActiveState updates their Clone, I'll remove
this wrapper.
AUTHOR
Michael K. Neylon <mneylon-pm@masemware.com>
COPYRIGHT
Copyright (c) 2001,2002 Michael K. Neylon. All rights reserved.
This library is free software. You can redistribute it and/or modify it under the same terms as Perl
itself.
perl v5.18.1 2013-11-03 Hash::Merge(3pm)