Perl：使用标量上下文取消引用数组？

Question

I have a strange issue with Perl and dereferencing.

I have an INI file with array values, under two different sections eg

[Common]
animals =<<EOT
dog
cat
EOT

[ACME]
animals =<<EOT
cayote
bird
EOT

I have a sub routine to read the INI file into an %INI hash and cope with multi-line entries.

I then use an $org variable to determine whether we use the common array or a specific organisation array.

@array = @{$INI{$org}->{animals}} || @{$INI{Common}->{animals}};

The 'Common' array works fine, ie if $org is anything but 'ACME' I get the values (dog cat) but if $org equals 'ACME'` I get a value of 2 back?

Any ideas??

Answer 1

Derefencing arrays is of course not forcing scalar context. But using || is. Therefore things like $val = $special_val || "the default"; $val = $special_val || "the default"; work just fine while your example doesn't.

Therefore @array will contain either a single number (the number of elements in the first array) or, if that is 0, the elements of the second array.

The perlop perldoc page even lists this example speficially:

In particular, this means that you shouldn't use this for selecting
between two aggregates for assignment:

    @a = @b || @c;              # this is wrong
    @a = scalar(@b) || @c;      # really meant this
    @a = @b ? @b : @c;          # this works fine, though

Depending on what you want, the solution could be:

my @array = @{$INI{$org}->{animals}}
   ? @{$INI{$org}->{animals}}
   : @{$INI{Common}->{animals}};