Inconsistency in misuse of "reverse" in list context [closed] - perl

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print reverse "word"; # prints 'word'
print reverse foreach ("word"); # prints nothing (empty string)
I am using Perl v5.24.
list context is forced by print, and these statements are "bad"
because reverse should be called in scalar contest to be useful.
Nevertheless, why the inconsistency?

Answer 1

print reverse foreach ("word"); # prints nothing (empty string)
What you have written is
for ( 'word' ) {
print reverse();
}
That code clearly executes the loop just once with $_ set to word, and prints a reversed empty list
Perhaps you should avoid statement modifiers until you are more familiar with the language
As tjd comments, reverse will reverse either a list or a string. In list context (as imposed by the call to print) it expects a list of parameters to reverse, and ignores $_. In scalar context it would just concatenate all parameters passed to it and reverse the resulting string; in the absence of any parameters it will reverse the string in $_

Answer 2

The reverse can indeed be used in either scalar context
perl -wE'$w = "hello"; $r = reverse $w; say $r' # olleh
or in list context
perl -wE'say join " ", reverse qw(hello there)' # there hello
Both are useful and there is no "inconsistency" in these behaviors.
One thing to watch out for is that when a list is used in scalar context
perl -wE'say scalar reverse qw(hello there)' # erehtolleh
then the list gets concatenated and reverse returns a string with characters in reverse order.
I am adding another "gotcha" for completeness, even as it has been covered in other answers.
The reverse defaults to $_ in scalar context, as expected. However, in list context it just doesn't take $_, and in for (#ary) { print reverse; }, with list context imposed on it by print, it has no arguments and thus prints nothing.

Answer 3

In scalar context, reverse reverses the characters of a string.
my $s = "abc";
$s = reverse($s);
say $s;
# cba
In list context, reverse reverses the scalars of its argument list.
my #a = qw( abc def ghi );
#a = reverse(#a);
say "#a";
# ghi def abc
Clearly, both uses are very consistent with each other. The only possible lack of consistency between scalar-context reverse and list-context reverse is what happens when you provide no argument expression. Scalar-context reverse defaults to using $_, but doing so would make no sense for list-context reverse, so it doesn't treat that case specially.
That means the reason print reverse for "word"; prints nothing is that the reverse of zero items is zero items.