Re^7: Perl list items

[AnomalousMonk]

in reply to Re^6: Perl list items
in thread Perl list items

my @c = combine(5,@n); # get array of arrays
my @A = @$c[0];        # get first sub-array

Because the 'precedence' (if that's the proper term here) of the  @ array dereference sigil is so high, the expression  @$c[0] attempts to dereference an array reference held in the  $c scalar (not in the  @c array) and then access the element at index 0 in the referenced array. (Update: Actually, my first thought was that  @$c[0] would look like a 'degenerate' array slice, like @x[0]; not sure why the appropriate warning was not generated.) The expression  @{ $c[0] } is what is needed in the given example.

>perl -wMstrict -MData::Dump -le
"my @c = (['x', 'y'], ['a', 'b'], ['c', 'd']);
 my $c = ['foo', 'bar'];
 ;;
 my @A1 = @  $c[0]  ;
 my @A2 = @{ $c[0] };
 dd \@A1;
 dd \@A2;
"
["foo"]

["x", "y"]

[Anonymous Monk]

To clarify  @$c[0] means the same as  @{$c}[0] meaning dereference $c, take array slice

So

 
$ perl -e " use Data::Dump; my $c = [qw/ a b c/]; dd @$c[1,2]; "
("b", "c")

While References quick reference lists this item explicitly (item 2), its somewhat documented in perlreftut/perlref but its not recommended

[AnomalousMonk]

To clarify @$c[0] means the same as @{$c}[0] meaning dereference $c, take array slice

Well... I'm not sure it's that much more clear. After all, "I know what I mean, ..."

I'm still puzzled by the absence of a "... better written as ..." warning. Maybe the usage is just too far off the beaten track for warnings to stumble over.

>perl -wMstrict -le
"my @c = ('foo');
 print @c[0];
 ;;
 my $c = ['bar'];
 print @{$c}[0];
 print @ $c [0];
"
Scalar value @c[0] better written as $c[0] at -e line 1.
foo
bar
bar

[Anonymous Monk]

I'm still puzzled by the absence of a "... better written as ..." warning.

Because the code is different :) Because @warnme... is different from @$derefNowarn...

For verbosity see diagnostics, try  perl -Mdiagnostics -e " @ARGV[0] "