1Tie::Hash::MultiValue(3U)ser Contributed Perl DocumentatiToine::Hash::MultiValue(3)
2
6 Tie::Hash::MultiValue - store multiple values per key
7
9 use Tie::Hash::MultiValue;
10 my $controller = tie %hash, 'Tie::Hash::MultiValue';
11 $hash{'foo'} = 'one';
12 $hash{'bar'} = 'two';
13 $hash{'bar'} = 'three';
14 # Fetch the values as references to arrays.
16 $controller->refs;
17 my @values = @{$hash{'foo'}}; # @values = ('one');
18 my @more = @{$hash{'bar'}}; # @more = ('two', 'three');
19 my @nothing = @{$hash{'baz'}}; # empty list if nothing there
20 # You can tie an anonymous hash as well.
22 my $hashref = {};
23 tie %$hashref, 'Tie::Hash::MultiValue';
24 $hashref->{'sample'} = 'one';
25 $hashref->{'sample'} = 'two';
26 # $hashref->{'sample'} now contains ['one','two']
27 # Iterate over the items stored under a key.
29 $controller->iterators;
30 while(my $value = $hash{bar}) {
31 print "bar: $value\n";
32 }
33 # prints
34 # bar: two
35 # bar: three
36
38 "Tie::Hash::MultiValue" allows you to have hashes which store their
39 values in anonymous arrays, appending any new value to the already-
40 existing ones.
41 This means that you can store as many items as you like under a single
43 key, and access them all at once by accessing the value stored under
44 the key.
45
47 See the synopsis for a typical usage.
48
50 None currently known.
51
53 Contact the author for support.
54
56 Joe McMahon
57 CPAN ID: MCMAHON
58 mcmahon@ibiblio.org
59 http://ibiblio.org/mcmahon
60
62 This program is free software; you can redistribute it and/or modify it
63 under the same terms as Perl itself.
64 The full text of the license can be found in the LICENSE file included
66 with this module.
67
69 Tie::Hash, perl(1), Perl Cookbook (1st version) recipe 13.15, program
70 13-5.
71
73 This class is a subclass of "Tie::ExtraHash"; it needs to override the
74 "TIEHASH" method to save the instance data (in $self->[1]), and the
75 "STORE" method to actually save the values in an anonymous array.
76 TIEHASH
78 If the 'unique' argument is supplied, we check to see if it supplies a
79 subroutine reference to be used to compare items. If it does, we store
80 that reference in the object describing this tie; if not, we supply a
81 function which simply uses 'eq' to test for equality.
82 The 'unique' function
84 This funtion will receive two scalar arguments. No assumption is made
86 about whether or not either argument is defined, nor whether these are
87 simple scalars or references. You can make any of these assumptions if
88 you choose, but you are responsible for checking your input.
89 You can perform whatever tests you like in your routine; you should
91 return a true value if the arguments are determined to be equal, and a
92 false one if they are not.
93 STORE
95 Push the value(s) supplied onto the list of values stored here. The
96 anonymous array is created automatically if it doesn't yet exist.
97 If the 'unique' argument was supplied at the time the hash was tied, we
99 will use the associated function (either yours, if you supplied one; or
100 ours, if you didn't) and only add the item or items that are not
101 present.
102 FETCH
104 Fetches the current value(s) for a key, depending on the current mode
105 we're in.
106 • 'refs' mode
108 Always returns an anonymous array containing the values stored
110 under this key, or an empty anonymous array if there are none.
111 • 'iterators' mode
113 If there is a single entry, acts just like a normal hash fetch. If
115 there are multiple entries for a key, we automatically iterate over
116 the items stored under the key, returning undef when the last item
117 under that key has been fetched.
118 Storing more elements into a key while you're iterating over it
120 will result in the new elements being returned at the end of the
121 list. If you've turned on 'unique', remember that they won't be
122 stored if they're already in the value list for the key.
123 NOTE: If you store undef in your hash, and then store other
125 values, the iterator will, when it sees your undef, return it
126 as a normal value. This means that you won't be able to tell
127 whether that's your undef, or the 'I have no more data here'
128 undef. Using 'list' or 'refs' mode is strongly suggested if you
129 need to store data that may include undefs.
130 Note that every key has its own iterator, so you can mix accesses
132 across keys and still get all the values:
133 my $controller = tie %hash, 'Tie::Hash::MultiValue';
135 $controller->iterators;
136 $hash{x} = $_ for qw(a b c);
137 $hash{y} = $_ for qw(d e f);
138 while ( my($x, $y) = ($hash{x}, $hash{y}) {
139 # gets (a,d) (b,e) (c,f)
140 }
141 iterators
143 Called on the object returned from tie(). Tells FETCH to return
144 elements one at a time each time the key is accessed until no more
145 element remain.
146 refs
148 Tells FETCH to always return the reference associated with a key. (This
149 allows you to, for instance, replace all of the values at once with
150 different ones.)
151 mode
153 Tells you what mode you're currently in. Does not let you change it!
154perl v5.36.0 2022-07-22 Tie::Hash::MultiValue(3)