Re: Re: Can this If/Else be condensed into a 1 liner with a trailing If?

the $in...

As you may or may not know, perl will return the last value in a subroutine it sees... so

sub foo {
  'foo';
}
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will return foo even without an explicit return 'foo';
so in a case like the following

print(foo(),"\n");

sub foo {
    if(1) {
        'foo';
    } else {
        'bar';
    }
}
[download]

foo will be printed, since it is the last real value perl saw in the subroutine, everything else was basically blank lines... BUT! one must be careful in this situation because if you ever come back and put code in after the if statement like

print(foo(),"\n");

sub foo {
    if(1) {
        'foo';
    } else {
        'bar';
    }
    print STDERR 'fooed';
}
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then you will get 1, the return value of a successful print. most people use an explicit return unless the value they are returning is the last line of the sub, since it is then much harder to miss.

- Ant
- Some of my best work - Fish Dinner

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Re: Re: Re: Can this If/Else be condensed into a 1 liner with a trailing If? by George_Sherston (Vicar) on Oct 03, 2001 at 10:25 UTC
Hmm. I thought it might be something like that, but now instead of a nebulous feeling that it must be something to do with returning values I actually know how it works! Very educational - thanks for the explanation. My subroutines will be grateful too. So (just getting this straight, hoping my thought processes won't be too dull for others) in jerrygarciuh's case, if he replaces the `if... else` with `print "$in was not a number!"; input() unless $in =~ /\d/;` [download] then the subroutine will return the number of characters `chomp`ed from `$in`, rather than `$in` itself. So in order to reduce the `if... else` loop to a single line, one wd have to do something like `sub input { my $arrayref=shift; print "\nSo far you've guessed @$arrayref." if $arrayref; print "\nWhat is your guess?\n"; chomp <STDIN>; my $in=<STDIN>; print "$in wasn't a number!";input() unless $in =~ /\d/; }` [download] Would that work? Is it nicer? Have I learnt something from this exchange? (The answer to at least one of these questions is "yes".) § George Sherston	[reply] [d/l] [select]
Re: Re: Re: Re: Can this If/Else be condensed into a 1 liner with a trailing If? by suaveant (Parson) on Oct 03, 2001 at 18:17 UTC
Actually, not quite... remember `print "$in wasn't a number!";input() unless $in =~ /\d/; # is the same as print "$in wasn't a number!"; input() unless $in =~ /\d/; # what you want is print("$in wasn't a number!"),input() unless $in =~ /\d/;` [download] See, with the comma, the unless contains the print and the input, with the ; it only contains the input(), and I'm not sure what will be returned in that case, so I would probably do... `print("$in wasn't a number!"),return input() unless $in =~ /\d/;` [download] Just to be safe. (It might work properly anyway, I'd have to test) It should return $in otherwise... I think... my rule of thumb usually is, if I am not sure what will be returned, I use a return. I usually only leave out the return when my value is on the actual last line of the subroutine. Can save headaches... :) - Ant - Some of my best work - Fish Dinner	[reply] [d/l] [select]