Backslash before subroutine call
Since I understood the difference between [] and \ in links, I used both the subroutine and the previous one, but when I tried later I thought it should give an error, but below is the program in perl
#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;
my @b;
for my $i ( 0 .. 10 ) {
$b[$i] = \somefunc($i);
}
print Dumper( \@b );
sub somefunc {
my $n = shift;
my ( @a, $k );
for my $j ( 11 .. 13 ) {
$k = $n * $j;
push( @a, $k );
}
print "a: @a \n";
return @a;
}
gives the result as:
a: 0 0 0
a: 11 12 13
a: 22 24 26
a: 33 36 39
a: 44 48 52
a: 55 60 65
a: 66 72 78
a: 77 84 91
a: 88 96 104
a: 99 108 117
a: 110 120 130
$VAR1 = [
\0,
\13,
\26,
\39,
\52,
\65,
\78,
\91,
\104,
\117,
\130
];
I was unable to figure out the way out. Give an explanation.
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What's going on here:
You are returning an array from somefunc
.
But you assign it to a scalar. What it does effectively, therefore, is simply putting the last value in the array into a scalar value.
my $value = ( 110, 120, 130 );
print $value;
When you do, $ value is set to the last value in the array. This is what actually happens in your code. See for example perldata
:
List values are denoted by separating individual values with commas (and enclosing the list in parentheses where precedence requires it):
(LIST)
In a context that does not require a list value, the value of what is represented by a list literal is simply the end element value, as for the C-comma operator. For example,
@foo = ('cc', '-E', $bar);
assigns the entire list value to the array
@foo
, but
foo = ('cc', '-E', $bar);
assigns the value of the variable $ bar to the scalar variable $ foo. Note that the value of the actual array in scalar context is the length of the array; the following assigns a value between 3 and $ foo:
@foo = ('cc', '-E', $bar);
$foo = @foo; # $foo gets 3
This is the last case that often occurs because it is a list in a scalar context.
And in your example - the backslash prefix denotes a reference to "- it's pretty much pointless because it's a number reference.
But for a scalar, it might be more meaningful:
my $newvalue = "fish";
my $value = ( 110, 120, 130, \$newvalue );
print Dumper $value;
$newvalue = 'barg';
print Dumper $value;
gives:
$VAR1 = \'fish';
$VAR1 = \'barg';
This is why you get results. The slash prefix means you are getting a result link, not a sub link. The link 130
doesn't really matter.
Usually, when you do the assignment above, you will get a warning about Useless use of a constant (110) in void context
, but this is not the case with the return of the subroutine.
If you want to insert a helper link, you need to add &
, but if you just want to insert the returned array by reference, you either need to:
$b[$i] = [somefunc($i)]
Or:
return \@a;
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