ЭЛЕКТРОННАЯ БИБЛИОТЕКА КОАПП |
Сборники Художественной, Технической, Справочной, Английской, Нормативной, Исторической, и др. литературы. |
11.3. Taking References to HashesProblemYou need to manipulate a hash by reference. This might be because it was passed into a function that way or because it's part of a larger data structure. SolutionTo get a hash reference: $href = \%hash; $anon_hash = { "key1" => "value1", "key2" => "value2", ... }; $anon_hash_copy = { %hash }; To dereference a hash reference: %hash = %$href; $value = $href->{$key}; @slice = @$href{$key1, $key2, $key3}; # note: no arrow! @keys = keys %$href; To check whether something is a hash reference: if (ref($someref) ne 'HASH') { die "Expected a hash reference, not $someref\n"; } DiscussionThis example prints out all the keys and values in two predefined hashes: foreach $href ( \%ENV, \%INC ) { # OR: for $href ( \(%ENV,%INC) ) { foreach $key ( keys %$href ) { print "$key => $href->{$key}\n"; } } Accessing slices of hashes by reference works just as it does with slices of arrays by reference. For example: @values = @$hash_ref{"key1", "key2", "key3"}; for $val (@$hash_ref{"key1", "key2", "key3"}) { $val += 7; # add 7 to each value in hash slice } See AlsoRecipe 5.0; Chapter 4 of Programming Perl; perlref (1); Recipe 11.9 |