symbolic reference & loading hashes

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

Hi people, I am having a little trouble getting this beauty to work :

trying to write a simple/good data loader for generic CSV files, I came up with this idea to specifically do it with symbolic links

I explain :

@test=(11,22,33,44);
@Fld=('LCD','XCOORD','Y','Name');
@Data{@Fld}=  @test;
print "Y($Data{'Y'}) N($Data{'LCD'})\n";
# until here all works fine

${$Fld[2]}=$test[2];  # <--- works
${$Fld[3]}=$test[3];  # <--- works
${@Fld}=@test;        # <--- does NOT work, why ?!
print "Y($Y) N($Name)\n";
[download]

thx in advance for any suggestion

kind regards

Comment on symbolic reference & loading hashes Download Code

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Re: symbolic reference & loading hashes by ikegami (Patriarch) on Jul 20, 2007 at 16:07 UTC
( Update: Oh! you are trying to create symbolic reference. Read Why it's stupid to `use a variable as a variable name' for why that's unwise. Use a hash instead, and then you can use the hash slice I mention below. ) I don't know what you are trying to do, but I'll point out two problems with that statement. You are assigning an array to a scalar. `${@Fld}=@test; ^ ^ \| \| scalar array` [download] An array evaluated in scalar context returns its length, so the length of the array would be assigned. `${@Fld}` doesn't make much sense. It looks like a dereference, but `@Fld` is not a reference. Since references are scalars, the dereference (`${...}`) expects a scalar value. `@Fld` evaluated in scalar context is its length, so `${@Fld}` is `${2}` aka `$2`. Maybe you are looking for a hash slice? `my @test=(11,22,33,44); my %Fld; @Fld{'LCD','XCOORD','Y','Name'} = @test; print($Fld{Y}, "\n"); # prints 33` [download]	[reply] [d/l] [select]
Re: symbolic reference & loading hashes by neosamuri (Friar) on Jul 20, 2007 at 16:01 UTC
I believe what you are looking for is: `@{@keys} = @values;` [download] ${...} is scalar, but the return you want is an array @rld is the keys in the package hash. @{...} takes keys and returns values. ${...} takes a key and returns a value.	[reply] [d/l]
Re^2: symbolic reference & loading hashes by ikegami (Patriarch) on Jul 20, 2007 at 16:39 UTC
Nope, that will evaluate @keys in scalar context in order to deref the value. Perl doesn't provide any direct means of setting multiple referenced values at once, so a loop is needed. `for my $i (0..$#keys) { ${$keys[$i]} = $values[$i]; }` [download] Alternatively, `use List::MoreUtils qw( pairwise ); pairwise { ${$a} = $b } @keys, @values;` [download] Of course, hashes are better than symbolic references. `@hash{@keys} = @values;` [download]	[reply] [d/l] [select]