Beefy Boxes and Bandwidth Generously Provided by pair Networks
We don't bite newbies here... much
 
PerlMonks  

Re: Re: Re: Re: Stumped on an array ref error...

by Madams (Monk)
on Oct 07, 2001 at 07:53 UTC ( #117270=note: print w/ replies, xml ) Need Help??


in reply to Re: Re: Re: Stumped on an array ref error...
in thread Stumped on an array ref error...

Thanks wog,

Your response about the exists operation lead me to really look at where the array ref is installed. I changed the following line (where ever it occured):

$cacheHOA{$sum}=($name);


to 2 separate lines:

$cacheHOA{$sum}=(); push @{$cacheHOA{$sum}}, $name;


and now it works, obviously i thought i was (in the one line version) assigning an annon array with one member, which also obviously did not work (why not?).

In the two line version i explicitly assigned an empty list and then pushed the member in.

Thanks for letting me bounce this off of y'all! Sometimes all you need is to have someone look at what your doing and say "Dude, you fscked that right here!"(points and smacks your head...)
_________________
madams@scc.net
(__) (\/) /-------\/ / | 666 || * ||----||


Comment on Re: Re: Re: Re: Stumped on an array ref error...
Select or Download Code
Re: Re: Re: Re: Re: Stumped on an array ref error...
by wog (Curate) on Oct 07, 2001 at 08:22 UTC
    $cacheHOA{$sum}=($name) assigns $name to $cacheHOA{$sum}. To actually create an arrayref you need to use []s instead, like $cacheHOA{$sum}=[$name].
Context is King
by chromatic (Archbishop) on Oct 07, 2001 at 21:49 UTC
    Scalar -> one, Array/List -> many.

    Take this line of code:

    $cacheHOA{$sum}=($name);
    There's a scalar on the left side and a one-element list on the right side. The left side determines the context. A hash value can only hold one thing, so it's scalar context. Perl evaluates the right side in scalar context.

    The Camel makes it abundantly clear that there is no general rule for this type of evaluation. Contrast these two snippets:

    $cacheHOA{$sum} = (1, 2, 3); $cacheHOA{$sum} = @values;
    The same goes for this line:
    $cacheHOA{$sum}=();
    Contextually, it's the same thing. The list is just empty this time. However, hash autovivification does the right thing afterwards because of the current value of $cacheHOA{$sum} at that point. (Assign '1' to it instead of an empty list and see the warning this next line throws.)
    push @{$cacheHOA{$sum}}, $name;
    Perl reads that as 'treat whatever is in $cacheHOA{$sum} as an array reference, and stick $name on the end'. Different context, since there's no scalar assignment on the left side.

    The trick is to make the right side of the assignment something that makes sense in scalar context. Since references are scalars, that's what you need. Either assign an array reference or an reference to an existing array.

    $cacheHOA{$sum} = []; $cacheHOA{$sum} = [$name]; $cacheHOA{$sum} = \@names;
    When you don't get what you expect, check the context.

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://117270]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others wandering the Monastery: (8)
As of 2014-09-16 10:48 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    How do you remember the number of days in each month?











    Results (9 votes), past polls