in search of a more elegant if then else

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: in search of a more elegant if then else by fullermd (Priest) on Feb 18, 2010 at 23:53 UTC
You can use the ternary operator `my $var = (condition) ? value1 : value2;` [download]	[reply] [d/l]
Re: in search of a more elegant if then else by toolic (Bishop) on Feb 18, 2010 at 23:53 UTC
The Conditional Operator is another way. You should decide, on a case-by-case basis, if it is better than an if/else. `my $var = (condition) ? value1 : value2;` [download]	[reply] [d/l]
Re: in search of a more elegant if then else by FunkyMonk (Chancellor) on Feb 19, 2010 at 11:10 UTC
As other Monks have suggested, the conditional operator does what you want. They have also pointed out that it can become difficult to read. However, if you set your code out carefully, the conditional operator can produce elegant and easy to read code. Consider: `my $n = 3; my $s = $n == 1 ? 'one' : $n == 2 ? 'two' : $n == 3 ? 'three' : $n == 4 ? 'four' : 'ETOOBIG'; print "$n : $s\n"; # 3 : three` [download] But, in some circumstances, you may be able to use a hash table: `my %h = ( 1 => 'one', 2 => 'two', 3 => 'three', 4 => 'four' ); $s = $h{$n} // 'ETOOBIG'; # needs perl 5.10 #$s = $h{$n} \|\| 'ETOOBIG'; # works for any perl print "$n : $s\n"` [download] See perlop for the difference between the or (`\|\|`) and defined or (`//`) operators Unless I state otherwise, all my code runs with strict and warnings	[reply] [d/l] [select]
Re^2: in search of a more elegant if then else by doug (Pilgrim) on Feb 19, 2010 at 16:11 UTC
And with 5.10 there is given/when `given ( $n ) { when ( 1 ) { $s = 'one'; } when ( 2 ) { $s = 'twe'; } when ( 3 ) { $s = 'three'; } when ( 4 ) { $s = 'four'; } default { $s = 'ETOOBIG'; } }` [download] - doug	[reply] [d/l]
Re^3: in search of a more elegant if then else by Anonymous Monk on Jan 16, 2011 at 22:31 UTC
i should read the changes more, i love this! so simple and easy to understand.	[reply]
Re: in search of a more elegant if then else by Anonymous Monk on Feb 18, 2010 at 23:52 UTC
It is not clumsy	[reply]
Re^2: in search of a more elegant if then else by Anonymous Monk on Feb 18, 2010 at 23:59 UTC
it may be correct syntax, but putting down 5 lines for something that can (now i've read comments) be done in one line seems a bit more elegant to me, and makes the code look a bit nicer.	[reply]
Re: in search of a more elegant if then else by Anonymous Monk on Feb 18, 2010 at 23:57 UTC
thanks for your help! i think this will make my code look a little better.. :-) what are the up's and downs of using the ternary operator?	[reply]
Re^2: in search of a more elegant if then else by ikegami (Patriarch) on Feb 19, 2010 at 00:11 UTC
It gets unreadable for all but the most trivial of expressions, but it's perfect for assigning one of two values to a variable. Also useful in that area are `# Use default when val is my $var = $val \|\| $default; # ... false (= stringifies to '' or '0'). my $var = $val // $default; # ... undefined. (Requires Perl 5.10.)` [download]	[reply] [d/l]
Re^3: in search of a more elegant if then else by fullermd (Priest) on Feb 19, 2010 at 06:34 UTC
It gets unreadable for all but the most trivial of expressions Right. It's possible to back yourself (or front yourself, if you're twisted :) into monstrosities with it. The classic C 12 Days of Christmas puts it to good (?) use, among its other distortions. Like a lot of things in perl (or any language, really), you just have to keep an eye on yourself to be sure you stay inside the lines. My two rules of thumb are length and nestedness: If I start nesting, that's a sign I should write it out in more explicit form If it starts getting much longer than 1 line, or there're more than maybe one or two logical ops (`&&`, `\|\|`, etc) in the condition, I should probably switch to if/else (None hard rules of course, but signs that I'm wandering off the beam and should take a step back to reevaluate)	[reply] [d/l] [select]
Re^2: in search of a more elegant if then else.. (ternary) by toolic (Bishop) on Feb 19, 2010 at 00:10 UTC
The Monastery has many opinions on this topic. Super Search where title contains "ternary": ?node_id=3989;HIT=ternary;re=N Mr. Ternary is greater than Mrs. If Else Ternary operators: a hinderance, not a help and others	[reply]
Re^2: in search of a more elegant if then else by aaron.m (Novice) on Feb 19, 2010 at 00:17 UTC
If it "fits," and is easy to read, use the ternary. Otherwise, use the if-then. Think in terms of which one will be easier to understand when someone else - ie. your boss - will be looking over your shoulder while you try to figure out a bug in something you wrote $x months or years ago. Be kind to yourself.	[reply]
Re^3: in search of a more elegant if then else by zebedee (Pilgrim) on Feb 19, 2010 at 09:07 UTC
I go for the Friday 4 p.m. test. It's broken, it's 4 p.m. on Friday, you've had a LOOONGGG week, and you want to think about going home. Which one is going to be easier to read and fix?	[reply]
Re^2: in search of a more elegant if then else by Xiong (Hermit) on Feb 19, 2010 at 13:51 UTC
You should note that the ternary operator and if-then-else don't do the same thing. The ternary operator is an operator, intended to return a value (which can be assigned, tested, or further operated upon). If-then-else executes one of two alternate blocks.	[reply]
Re^3: in search of a more elegant if then else by BrowserUk (Patriarch) on Feb 19, 2010 at 14:08 UTC
Just to blur the lines a little :) `print do{ if( $_ ) { 'fred' }else{ 'bill' } } for 0, 1;; bill fred` [download] Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice. "I'd rather go naked than blow up my ass"	[reply] [d/l]
Re^4: in search of a more elegant if then else by TimToady (Parson) on Feb 20, 2010 at 16:33 UTC
Re^5: in search of a more elegant if then else by BrowserUk (Patriarch) on Feb 20, 2010 at 17:25 UTC
Some notes below your chosen depth have not been shown here
Re: in search of a more elegant if then else by Anonymous Monk on Feb 19, 2010 at 19:03 UTC
A more general question is: what are you computing with this if statement? If it's something interesting and complex, think about whether or not you can factor out some or all the functionality into it's own function, so you can re-use it elsewhere, and test it independently. If it's something simple, then the number of lines you need to code it won't really matter. For example, it's probably better to use this for a complicated condition: `$score = skatingScore($technique, $interpretation, isRussian($judge) ) +;` [download] but you can use something like this for a simple one... `$ranking = $isDisqualified ? "N/A" : rank($score);` [download] -- AC	[reply] [d/l] [select]
Re: in search of a more elegant if then else by rir (Vicar) on Feb 22, 2010 at 13:24 UTC
There is also shellish short circuiting. (I can't say that fast.) `$var = "condition_false"; $condition and $var = "condition_true;` [download] Be well, rir	[reply] [d/l]