Re^2: conditional print. Is correct to use it?

... a FALSE value can be "non empty", so || is probably not the best choice.

I don't understand this statement. (Update: hippo has likely shown the way to understanding. :) Is there any false value of $x, empty or not, for which the expression ($x || $y) would not evaluate as the value of $y? Likewise, given the statement
$x ||= $y;
is there any false initial value of $x for which the final value of $x would not end up as $y?

Give a man a fish: <%-{-{-{-<

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Re^3: conditional print. Is correct to use it? by hippo (Archbishop) on Oct 28, 2020 at 21:19 UTC
I think kcott is saying that you might, in some conditions, wish to retain the non-empty false value in $x rather than discard it in favour of $y. eg. if 0 were a valid input for $x and you had: `$x = 0; $y = 10; $number = $x \|\| $y; print "$number\n";` [download] You would see 10 rather than the valid-but-false 0. In such cases `$number = $x // $y;` might be more appropriate. 🦛	[reply] [d/l] [select]
Re^3: conditional print. Is correct to use it? by kcott (Archbishop) on Oct 29, 2020 at 03:50 UTC
Pretty much what ++hippo said. :-) length will return FALSE for both `''` and `undef`, and TRUE for both `0` and `'0'`. It's first documented as doing that in 5.12.0; however, there was a bug that was fixed in 5.14.0 (perl5140delta: Syntax/Parsing Bugs) so I'd be more comfortable with both `defined` and `length` if using anything earlier than 5.14.0. # 5.14.0 or later $ perl -E 'my ($x, $y) = (0, "fallback"); $x = length $x ? $x : $y; sa +y $x' 0 $ perl -E 'my ($x, $y) = ("0", "fallback"); $x = length $x ? $x : $y; +say $x' 0 $ perl -E 'my ($x, $y) = ("", "fallback"); $x = length $x ? $x : $y; s +ay $x' fallback $ perl -E 'my ($x, $y) = (undef, "fallback"); $x = length $x ? $x : $y +; say $x' fallback # 5.12.0 or earlier $ perl -E 'my ($x, $y) = (0, "fallback"); $x = (defined $x && length $ +x) ? $x : $y; say $x' 0 $ perl -E 'my ($x, $y) = ("0", "fallback"); $x = (defined $x && length + $x) ? $x : $y; say $x' 0 $ perl -E 'my ($x, $y) = ("", "fallback"); $x = (defined $x && length +$x) ? $x : $y; say $x' fallback $ perl -E 'my ($x, $y) = (undef, "fallback"); $x = (defined $x && leng +th $x) ? $x : $y; say $x' fallback # Probably not what was intended $ perl -E 'my ($x, $y) = ("0", "fallback"); $x \|\|= $y; say $x' fallback $ perl -E 'my ($x, $y) = ("", "fallback"); $x //= $y; say "<$x>"' <> [download] — Ken	[reply] [d/l] [select]