Dereferencing array of hashrefs

Guildencrantz has asked for the wisdom of the Perl Monks concerning the following question:

Okay, I'm trying to dereference an array of hash refs, and I can do it. But it takes two statements! The horror is mind boggling.
I think I've been staring at this too long and now I need help. My working code is this:

my $rowhash = (fetchrow_hashref($dbh, $query))[0];
print $$rowhash{'Msg_type'}, "\n";
[download]

and it works just fine. I get the hashed value that I'm looking for. My question is: Can't this be done on a single line? Can't I dereference the fetchrow() return all at once? I've been playing with this for a while and can't seem to get it to work.
Thanks for your shared wisdom,
~~Guildencrantz

Comment on Dereferencing array of hashrefs Download Code

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Re: Dereferencing array of hashrefs by blokhead (Monsignor) on May 12, 2004 at 23:52 UTC
The expression `(fetchrow_hashref($dbh, $query))[0]` evaluates to a hashref. You can dereference a key from any hashref by using `EXPR->{key}`. You can also omit the arrow operator if EXPR ends with an array or hash index. Putting that together gives: `print +(fetchrow_hashref($dbh, $query))[0]{key}, "\n";` [download] You need the + to disambiguate the expression from `print()`. All in all, it's a little messy, and having the extra variable is a reasonable tradeoff for readability. Update: ysth is dead on, you do need the arrow! blokhead	[reply] [d/l] [select]
Re: Re: Dereferencing array of hashrefs by ysth (Canon) on May 13, 2004 at 02:37 UTC
You can also omit the arrow operator if EXPR ends with an array or hash index. An array or hash index, yes, but not a list slice; here you do need the ->.	[reply]
Re: Re: Dereferencing array of hashrefs by Guildencrantz (Sexton) on May 13, 2004 at 02:13 UTC
Thanks! I would like to note that your consolidated version isn't working. It keeps kicking the error: `syntax error at ./script.pl line 43, near "){" Execution of ./script.pl aborted due to compilation errors.` [download] However the expanded EXPR->{key} version works fabulously. I do agree that it's a bit ambiguous, but I find it more fitting in this particular instance. Again, thanks. ~~Guildencrantz	[reply] [d/l]