How can I use an array as a hash value in Perl?

Question

Ok, so here's the entire structure I'm trying to create. I need to create an anonymous array that I can use as a hash value. This works in my program:

$result = {
    count, 2,
    elementList, [
        {name => "John Doe", age => 23},
        {name => "Jane Doe", age => 24}
    ]
};

I'm trying to create the exact same thing with code like this. This works:

my @elements = [
     {name => "John Doe", age => 23},
     {name => "Jane Doe", age => 24}
];

$result = {
    count, 2,
    elementList, @elements
};

But this does NOT work:

my @elements;
push(@elements, {name => "John Doe", age => 23});
push(@elements, {name => "Jane Doe", age => 24});

$result = {
    count, 2,
    elementList, @elements
};

Answer 1

You are assigning an array reference (the [] syntax) to your array. As a first and only element since you don't specify any others.

You wanted to directly assign a list there, using parentheses () instead of the square brackets.

Check out perldsc for an introduction on the subject.

Answer 2

Wrong brackets.

You actually need to build a structure like this:

my @elements = (
    {name => "John Doe", age => 23},
    {name => "Jane Doe", age => 24}
);

To do it in a loop, you will need to modify this code:

my @elements;  # same as my @elements = ();
push(@elements, {name => "John Doe", age => 23});
push(@elements, {name => "Jane Doe", age => 24});

The reason is that the square brackets build a reference to an array. A reference to an array is not the same thing as an array.

To make a list of elements to assign to an array, use round brackets ().

Answer 3

[] makes a reference to an empty array. You are creating an array with one element. Just say:my @elements; to make an empty array.

Answer 4

As others have mentioned, you're describing an unusual data structure: an array with only one element, which is an arrayref of hashrefs. I'll assume that you really do want that structure for some reason.

my @elements = [
    {name => "John Doe", age => 23},
    {name => "Jane Doe", age => 24}
];

is equivalent to

my @elements = [];
push(@{ $elements[0] }, {name => "John Doe", age => 23});
push(@{ $elements[0] }, {name => "Jane Doe", age => 24});

because you want to push the hashrefs onto the arrayref in $elements[0], not the @elements array.

But it's unusual to have an array with only one element. Looking at the additional code you've posted, what you really want is this:

my $elementsRef = [];
push(@$elementsRef, {name => "John Doe", age => 23});
push(@$elementsRef, {name => "Jane Doe", age => 24});

Or this:

my @elements;
push(@elements, {name => "John Doe", age => 23});
push(@elements, {name => "Jane Doe", age => 24});

and then use \@elements where you currently use @elements.

Either one of those will work. It's up to you to decide which one you prefer. I'd probably go with the second version.