Hash::Layout - hashes with predefined levels, composite keys and default values


 use Hash::Layout;
 # Create new Hash::Layout object with 3 levels and unique delimiters:
 my $HL = Hash::Layout->new({
  levels => [
    { delimiter => ':' },
    { delimiter => '/' }, 
    {}, # <-- last level never has a delimiter
 # load using actual hash structure:
   '*' => {
     '*' => {
       foo_rule => 'always deny',
       blah     => 'thing'
     NewYork => {
       foo_rule => 'prompt'
 # load using composite keys:
   'Office:NewYork/foo_rule' => 'allow',
   'Store:*/foo_rule'        => 'other',
   'Store:London/blah'       => 'purple'
 # load composite keys w/o values (uses default_value):
 $HL->load(qw/baz:bool_key flag01/);
 # get a copy of the hash data:
 my $hash = $HL->Data;
 #  $hash now contains:
 #    {
 #      "*" => {
 #        "*" => {
 #          blah => "thing",
 #          flag01 => 1,
 #          foo_rule => "always deny"
 #        },
 #        NewYork => {
 #          foo_rule => "prompt"
 #        }
 #      },
 #      Office => {
 #        NewYork => {
 #          foo_rule => "allow"
 #        }
 #      },
 #      Store => {
 #        "*" => {
 #          foo_rule => "other"
 #        },
 #        London => {
 #          blah => "purple"
 #        }
 #      },
 #      baz => {
 #        "*" => {
 #          bool_key => 1
 #        }
 #      }
 #    }
 # lookup values by composite keys:
 $HL->lookup('*:*/foo_rule')              # 'always deny'
 $HL->lookup('foo_rule')                  # 'always deny'
 $HL->lookup('ABC:XYZ/foo_rule')          # 'always deny'  # (virtual/fallback)
 $HL->lookup('Lima/foo_rule')             # 'always deny'  # (virtual/fallback)
 $HL->lookup('NewYork/foo_rule')          # 'prompt'
 $HL->lookup('Office:NewYork/foo_rule')   # 'allow'
 $HL->lookup('Store:foo_rule')            # 'other'
 $HL->lookup('baz:Anything/bool_key')     # 1              # (virtual/fallback)
 # lookup values by full/absolute paths:
 $HL->lookup_path(qw/ABC XYZ foo_rule/)   # 'always deny'  # (virtual/fallback)
 $HL->lookup_path(qw/Store * foo_rule/)   # 'other'


Hash::Layout provides deep hashes with a predefined number of levels which you can access using special "composite keys". These are essentially string paths that inflate into actual hash keys according to the defined levels and delimiter mappings, which can be the same or different for each level. This is useful both for shorter keys as well as merge/fallback to default values, such as when defining overlapping configs ranging from broad to narrowing scope (see example in SYNOPIS above).

This module is general-purpose, but was written specifically for the flexible filter() feature of DBIx::Class::Schema::Diff, so refer to its documentation as well for a real-world example application. There are also lots of examples and use scenarios in the unit tests under t/.



Create a new Hash::Layout instance. The following build options are supported:


Required. ArrayRef of level config definitions, or a numeric number of levels for default level configs. Each level can define its own delimiter (except the last level) and list of registered_keys, both of which are optional and determine how ambiguous/partial composite keys are resolved.

Level-specific delimiters provide a mechanism to supply partial paths in composite keys but resolve to a specific level. The word/string to the left of a delimiter character that is specific to a given level is resolved as the key of that level, however, the correct path order is required (keys are only tokenized in order from left to right).

Specific strings can also be declared to belong to a particular level with registered_keys. This also only effects how ambiguity is resolved with partial composite keys. See also the no_fill and no_pad options.

See the unit tests for examples of exactly how this works.

Internally, the level configs are coerced into Hash::Layout::Level objects.

For Hash::Layouts that don't need/want level-specific delimiters, or level-specific registered_keys, a simple integer value can be supplied instead for default level configs all using / as the delimiter.

So, this:

 my $HL = Hash::Layout->new({ levels => 5 });

Is equivalent to:

 $HL = Hash::Layout->new({
  levels => [
    { delimiter => '/' }
    { delimiter => '/' }
    { delimiter => '/' }
    { delimiter => '/' }
    {} #<-- last level never has a delimiter

levels is the only required parameter.


Value to assign keys when supplied to load() as simple strings instead of key/value pairs. Defaults to the standard bool/true value of 1.


Value to use for the key for levels which are not specified, as well as the key to use for default/fallback when looking up non-existant keys (see also lookup_mode). Defaults to a single asterisk (*).


If true, partial composite keys are not expanded with the default_key (in the middle) to fill to the last level. Defaults to 0.


If true, partial composite keys are not expanded with the default_key (at the front or middle) to fill to the last level. no_pad implies no_fill. Again, see the tests for a more complete explanation. Defaults to 0.


If true, values at the bottom level are allowed to be hashes, too, for the purposes of addressing the deeper paths using composite keys (see deep_delimiter below). Defaults to 1.


When allow_deep_values is enabled, the deep_delimiter character is used to resolve composite key mappings into the deep hash values (i.e. beyond the predefined levels). Must be different from the delimiter used by any of the levels. Defaults to a single dot (.).

For example:


One of either get, fallback or merge. In fallback mode, when a non-existent composite key is looked up, the value of the first closest found key path using default keys is returned instead of undef as is the case with get mode. merge mode is like fallback mode, except hashref values are merged with matching default key paths which are also hashrefs. Defaults to merge.


If true, key value lookup calls will automatically try to match wildcard (text glob) expressions. Defaults to false (0).


Returns a new/cloned Hash::Layout instance


Dynamic method coerces supplied value into a new Hash::Layout instance with a new set of loaded data. See unit tests for more info.


CodeRef wrapper around coerce(), suitable for use in a Moo-compatible attribute declaration


Loads new data into the hash.

Data can be supplied as hashrefs with normal/local keys or composite keys, or both. Composite keys can also be supplied as sub-keys and are resolved relative to the location in which they appear as one would expect.

Composite keys can also be supplied as simple strings w/o corresponding values in which case their value is set to whatever default_value is set to (which defaults to 1).

See the unit tests for more details and lots of examples of using load().


Simpler alternative to load(). Expects exactly two arguments as standard key/values.


Converts a composite key string into its full path and returns it as a list. Called internally wherever composite keys are resolved.


Inverse of resolve_key_path; takes a path as a list and returns a single composite key string (i.e. joins using the delimiters for each level). Obviously, it only returns fully-qualified, non-ambiguous (not partial) composite keys.


Returns true if the supplied composite key exists and false if it doesn't. Does not consider default/fallback key paths.


Like exists(), but requires the key to be supplied as a resolved/fully-qualified path as a list of arguments. Used internally by exists().


Retrieves the real value of the supplied composite key, or undef if it does not exist. Use exists() to distinguish undef values. Does not consider default/fallback key paths (that is what lookup() is for).


Like get(), but requires the key to be supplied as a resolved/fully-qualified path as a list of arguments. Used internally by get().


Returns the value of the supplied composite key, falling back to default key paths if it does not exist, depending on the value of lookup_mode.

If the lookup_mode is set to 'get', lookup() behaves exactly the same as get().

If the lookup_mode is set to 'fallback' and the supplied key does not exist, lookup() will search the hierarchy of matching default key paths, returning the first value that exists.

If the lookup_mode is set to 'merge', lookup() behaves the same as it does in 'fallback' mode for all non-hashref values. For hashref values, the hierarchy of default key paths is searched and all matches (that are themselves hashrefs), including the exact/lowest value itself, are merged and returned.


Like lookup(), but requires the key to be supplied as a resolved/fully-qualified path as a list of arguments. Used internally by lookup().


Like lookup_path(), but only returns the value if it is a "leaf" (i.e. not a hashref with deeper sub-values). Empty hashrefs ({}) are also considered leaf values.


Like lookup_path(), but matches/returns by comparing a full composite key string with wildcard (text glob) expressions.


Deletes the supplied composite key and returns the deleted value, or undef if it does not exist. Does not consider default/fallback key paths, or delete multiple items at once (e.g. like the Linux rm command does with shell globs).


Like delete(), but requires the key to be supplied as a resolved/fully-qualified path as a list of arguments. Used internally by delete().


Returns a read-only (i.e. cloned) copy of the full loaded hash structure.


Returns the number of levels defined for this Hash::Layout instance.


Returns a hashref of all the keys that have been loaded/exist for the supplied level index (the first level is at index 0).


Debug method. Returns a list of all the default key paths as a list of bitmasks (in binary/string form). Any key path which has at least one default key at any level is considered a default path and is indexed as a bitmask, with '1' values representing the default key position(s). For instance, the key path {*}{*}{foo_rule} from the 3-level example from the SYNOPSIS is indexed as the bitmask 110 (6 in decimal).

These bitmasks are used internally to efficiently search for and properly order default key values for quick fallback/merge lookups, even when there are a very large number of levels (and thus very, VERY large number of possible default paths). That is why they are tracked and indexed ahead of time.

This is a debug method which should not be needed to be used for any production code. I decided to leave it in just to help document some of the internal workings of this module.


Clears and removes all loaded data and resets internal key indexes and counters.


For more examples, see the following:


Henry Van Styn <>


This software is copyright (c) 2014 by IntelliTree Solutions llc.

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