Question about arrays of hashes

[Steve]

Forgive a newbie question, but I'm hoping that someone can shed some
light for me on weirdness I'm seeing when trying to access a particular
hash from an array-of-hashes. I had a lot of difficulty assigning a
particular element to its own variable, but after some experimentation I
found that this works:


my @array = MyModule->getArrayOfHashes();
my $hash = $array[$index];
%hash = %$hash;


I have to first create the variable in scalar context, then do a funky
dereferencing thing while changing the context to hash. For one thing,
I'd like to better understand what is really going on here... I just
stumbled across this solution through experimentation and dumb luck, I
don't really understand it. Secondly, I'm wondering if there's some
shorthand technique for doing this that doesn't require three lines of
code. Thanks in advance!

 

[Damian Lukowski]

my @array = MyModule->getArrayOfHashes();
my $hash = $array[$index];
%hash = %$hash;

Get n'th hash-Reference from the array: (MyModule->getArrayOfHashes())[n]

Get value of hash-key 'foo' from n'th hash-reference from the array:
(MyModule->getArrayOfHashes())[n]->{'foo'}

 

[Gunnar Hjalmarsson]

Forgive a newbie question, but I'm hoping that someone can shed some
light for me on weirdness I'm seeing when trying to access a particular
hash from an array-of-hashes. I had a lot of difficulty assigning a
particular element to its own variable, but after some experimentation I
found that this works:

my @array = MyModule->getArrayOfHashes();
my $hash = $array[$index];
%hash = %$hash;

I have to first create the variable in scalar context, then do a
funky dereferencing thing while changing the context to hash. For one
thing, I'd like to better understand what is really going on here...

perldoc perlref

I'm wondering if there's some shorthand technique for doing this that
doesn't require three lines of code.

What's "this"? Copying one of the hashes to a named hash?

my %hash = %{ $array[$index] };

Or assigning a value to one of the anonymous hashes?

$array[$index]->{somekey} = 'somevalue';

 

[xhoster]

Forgive a newbie question, but I'm hoping that someone can shed
some light for me on weirdness I'm seeing when trying to access a
particular hash from an array-of-hashes. I had a lot of difficulty
assigning a particular element to its own variable, but after some
experimentation I found that this works:

my @array = MyModule->getArrayOfHashes();
my $hash = $array[$index];
%hash = %$hash;

I have to first create the variable in scalar context, then do a
funky dereferencing thing while changing the context to hash. For one
thing, I'd like to better understand what is really going on here... I
just stumbled across this solution through experimentation and dumb luck,
I don't really understand it.

See the "perldoc"s for perlref, perlreftut, and perldsc. I don't how to
describe it better than they do. (If I did, I would propose replacing them
with my better description.)

Secondly, I'm wondering if there's some
shorthand technique for doing this that doesn't require three lines of
code. Thanks in advance!

You need get the right element out of the list, which you do by
subscripting the list with the ()[] form:

my $hashref = (MyModule->getArrayOfHashes())[$index];

Although this does seem strange for me for semantic rather than syntactic
reasons. It seems like an odd OO module design that would lead me to
already know which index I want from a list when I don't yet have the list
but need to go to the module to get it. I know that is the way things work
with things like the "stat" function, but the stat function isn't OO.

Then you need to dereference that, which you do by %{} form:

my %hash=%{(MyModule->getArrayOfHashes())[$index]};

Although 90+% of the time, I would just get the $hashref and dereference
it as needed, rather than making a dereferenced copy up-front.

Xho

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