arrays and dot operator

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

Perl noob, coming in from Python and Bash. Reading the llama book, in the bit about arrays, and noted something...unexpected.

@array = 5..9;             # this section works as expected
print @array;             # 56789
print "\n";
$fred = pop(@array);
print $fred;             # 9
print "\n"; 
print @array;             # 5678
print "\n";    

@new_array = 1..5;            # this section does not
print @new_array . "\n";    # 5
$barney = pop(@new_array);    
print $barney . "\n";        # 5
print @new_array . "\n";    # 4
print "\n";
[download]

In the first section I'm getting the contents of the array and in the second the size of the array, seemingly based on how I'm using the newlines. Is this some odd anomaly or intended functionality? Am I missing something? regards, Richard

Comment on arrays and dot operator Download Code

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Re: arrays and dot operator by vrk (Chaplain) on Apr 05, 2017 at 14:06 UTC
It's not a newline problem. In your second section, the line `print @new_array . "\n"` has `@new_array` in scalar context, because the string concatenation operator (.) puts its arguments in scalar context. The line is actually executed as `print scalar(@new_array) . "\n"`. In scalar context, you get the array length, which is 5 in this case. If you want to print a newline after the array, just use a comma: `print @new_array, "\n";` [download]	[reply] [d/l] [select]
Re^2: arrays and dot operator by BillKSmith (Monsignor) on Apr 05, 2017 at 14:59 UTC
Or use: `#print "@array,\n"; print "@array\n";` [download] This will print the array elements separated by the contents of $" (space by default), followed by the newline. Update: Removed comma as indicated by vrk Bill	[reply] [d/l]
Re^3: arrays and dot operator by vrk (Chaplain) on Apr 06, 2017 at 12:05 UTC
You have an extra comma there.	[reply]
Re: arrays and dot operator by haukex (Archbishop) on Apr 05, 2017 at 14:20 UTC
vrk has already answered your question, I just wanted to give a tip: don't use arrays of numbers to test things like this, otherwise it's hard to tell when the array in scalar context is returning the size of the array. `my @new_array = 'a'..'e'; print @new_array . "\n"; # "5" print pop(@new_array) . "\n"; # "e" print @new_array . "\n"; # "4" print @new_array , "\n"; # "abcd"` [download]	[reply] [d/l]
Re: arrays and dot operator by thanos1983 (Parson) on Apr 05, 2017 at 14:22 UTC
Hello rkappler, Welcome to the community, regarding the non expecting behavior the monks already provided you with wisdom. Just another idea on printing an array and complex data, I use Data::Dumper: `#!/usr/bin/perl use strict; use warnings; use Data::Dumper; my @new_array = 1 .. 5; print Dumper \@new_array; __END__ $ perl test.pl $VAR1 = [ 1, 2, 3, 4, 5 ];` [download] Take a look also here (How do I output each Perl array element sourrounded in quotes?). Hope this helps. Seeking for Perl wisdom...on the process of learning...not there...yet!	[reply] [d/l]
Re: arrays and dot operator by huck (Prior) on Apr 05, 2017 at 14:02 UTC
`print @new_array . "\n";` uses @new_array in a scalar reference `print @new_array , "\n";` uses @new_array in an "wantarray" reference	[reply] [d/l] [select]
Re^2: arrays and dot operator by haukex (Archbishop) on Apr 05, 2017 at 14:27 UTC
scalar reference ... "wantarray" reference The correct terms are "scalar context" and "list context". For the OP, some references: Context tutorial, It's all about context, "Context" in Modern Perl.	[reply]
Re: arrays and dot operator by rkappler (Initiate) on Apr 05, 2017 at 14:11 UTC
I understand (or at least think I do, off to run some test scripts to be sure). Either I missed that bit in the book or it wasn't (yet?) addressed. Thanks for the help!!!	[reply]
Re: arrays and dot operator by rkappler (Initiate) on Apr 05, 2017 at 14:01 UTC
Forgot to add... using perl 5.14 on Win10 - work box, not by choice :-)	[reply]


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