NAME¶
Hash::Flatten - flatten/unflatten complex data hashes
SYNOPSIS¶
# Exported functions
use Hash::Flatten qw(:all);
$flat_hash = flatten($nested_hash);
$nested_hash = unflatten($flat_hash);
# OO interface
my $o = new Hash::Flatten({
HashDelimiter => '->',
ArrayDelimiter => '=>',
OnRefScalar => 'warn',
});
$flat_hash = $o->flatten($nested_hash);
$nested_hash = $o->unflatten($flat_hash);
DESCRIPTION¶
Converts back and forth between a nested hash structure and a flat hash of
delimited key-value pairs. Useful for protocols that only support key-value
pairs (such as CGI and DBMs).
Functional interface¶
- $flat_hash = flatten($nested_hash, \%options)
- Reduces a nested data-structure to key-value form. The
top-level container must be hashref. For example:
$nested = {
'x' => 1,
'y' => {
'a' => 2,
'b' => 3
},
'z' => [
'a', 'b', 'c'
]
}
$flat = flatten($nested);
use Data::Dumper;
print Dumper($flat);
$VAR1 = {
'y.a' => 2,
'x' => 1,
'y.b' => 3,
'z:0' => 'a',
'z:1' => 'b',
'z:2' => 'c'
};
The "\%options" hashref can be used to override the default
behaviour (see "OPTIONS").
- $nested_hash = unflatten($flat_hash, \%options)
- The unflatten() routine takes the flattened hash and
returns the original nested hash (see "CAVEATS" though).
OO interface¶
- $o = new Hash::Flatten(\%options)
- Options can be squirreled away in an object (see
"OPTIONS")
- $flat = $o->flatten($nested)
- Flatten the structure using the options stored in the
object.
- $nested = $o->unflatten($flat)
- Unflatten the structure using the options stored in the
object.
OPTIONS¶
- HashDelimiter and ArrayDelimiter
- By default, hash dereferences are denoted by a dot, and
array dereferences are denoted by a colon. However you may change these
characters to any string you want, because you don't want there to be any
confusion as to which part of a string is the 'key' and which is the
'delimiter'. You may use multicharacter strings if you prefer.
- OnRefScalar and OnRefRef and OnRefGlob
- Behaviour if a reference of this type is encountered during
flattening. Possible values are 'die', 'warn' (default behaviour but
warns) or a coderef which is passed the reference and should return the
flattened value.
By default references to references, and references to scalars, are followed
silently.
- EscapeSequence
- This is the character or sequence of characters that will
be used to escape the hash and array delimiters. The default escape
sequence is '\\'. The escaping strategy is to place the escape sequence in
front of delimiter sequences; the escape sequence itself is escaped by
replacing it with two instances.
- DisableEscapes
- Stop the escaping from happening. No escape sequences will
be added to flattened output, nor interpreted on the way back.
WARNING: If your structure has keys that contain the delimiter
characters, it will not be possible to unflatten the structure
correctly.
CAVEATS¶
Any blessings will be discarded during flattening, so that if you flatten an
object you must re-
bless() it on unflattening.
Note that there is no delimiter for scalar references, or references to
references. If your structure to be flattened contains scalar, or reference,
references these will be followed by default, i.e. "'foo' =>
\\\\\\$foo" will be collapsed to "'foo' => $foo". You can
override this behaviour using the OnRefScalar and OnRefRef constructor option.
Recursive structures are detected and cause a fatal error.
SEE ALSO¶
The perlmonks site has a helpful introduction to when and why you might want to
flatten a hash:
http://www.perlmonks.org/index.pl?node_id=234186
- CGI::Expand
- Unflattens hashes using "." as a delimiter,
similar to Template::Toolkit's behaviour.
- Tie::MultiDim
- This provides a tie interface to unflattening a data
structure if you specify a "template" for the structure of the
data.
- MLDBM
- This also provides a tie interface but reduces a nested
structure to key-value form by serialising the values below the top
level.
VERSION¶
$Id: Flatten.pm,v 1.19 2009/05/09 12:42:02 jamiel Exp $
AUTHOR¶
John Alden & P Kent <cpan _at_ bbc _dot_ co _dot_ uk>
COPYRIGHT¶
(c) BBC 2005. This program is free software; you can redistribute it and/or
modify it under the GNU GPL.
See the file COPYING in this distribution, or
http://www.gnu.org/licenses/gpl.txt