long if statements... What's the best way?

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

Replies are listed 'Best First'.
Re: long if statements... What's the best way? by kyle (Abbot) on Apr 02, 2008 at 15:59 UTC
If you're really checking for `$var` being `eq` to one of many elements, a hash would work. `my %look_for = map { $_ => 1 } qw( a b ... ); if ( $look_for{ $var } ) { }` [download] That said, I don't see anything wrong with using a regular expression, if it does what you want. I'd only think grep is a problem if you have a huge number of items to check. Maybe you want `List::Util::first` here?	[reply] [d/l] [select]
Re: long if statements... What's the best way? by Narveson (Chaplain) on Apr 02, 2008 at 16:18 UTC
Don't worry about performance just yet. Write something that is easy for you to maintain in case you change the list of alternatives. `my @alternatives = qw(a b etc); # add more by just typing them if (grep {$_ eq $var} @alternatives) {}` [download]	[reply] [d/l]
Re: long if statements... What's the best way? by wade (Pilgrim) on Apr 02, 2008 at 15:59 UTC
When something looks like that, I use a regex: `if ($var =~ /^[ab...]$/)` [download] -- Wade	[reply] [d/l]
Re: long if statements... What's the best way? (STRING ~~ ARRAY) by lodin (Hermit) on Apr 02, 2008 at 19:17 UTC
If you have Perl 5.10 you can do `if ($var ~~ [ 'a', 'b', ... ]) { ... }` [download] or `my @ok = ('a', 'b', ...); if ($var ~~ @ok) { ... }` [download] This is more efficient than `grep` because it doesn't try to match every element. In earlier versions you can do `my %ok = map { $_ => 1 } 'a', 'b', ...; if ($ok{$var}) { ... }` [download] lodin	[reply] [d/l] [select]
Re: long if statements... What's the best way? by nedals (Deacon) on Apr 02, 2008 at 17:26 UTC
Similar to wade's solution, but with multi-character comparision `if ($var=~/^(apple\|pear\|orange)$/) {....` [download]	[reply] [d/l]
Re: long if statements... What's the best way? by casiano (Pilgrim) on Apr 02, 2008 at 19:14 UTC
Just one more way to do it: use `first` from `List::util` `lhp@nereida:~/Lperl/src/cookbook/ch16$ perl -wde 0 main::(-e:1): 0 DB<1> use List::Util qw(first) DB<2> $var = 'd' DB<3> print "Found $var\n" if (first { $_ eq $var } qw{a e g h d r}) Found d DB<4> $var = 'x' DB<5> print "Found $var\n" if (first { $_ eq $var } qw{a e g h d r}) DB<6>` [download] Cheers Casiano	[reply] [d/l] [select]
Re^2: long if statements... What's the best way? by Herkum (Parson) on Apr 02, 2008 at 19:45 UTC
any would make more sense in this context. Otherwise the end result is the same.	[reply]
Re^2: long if statements... What's the best way? by lodin (Hermit) on Apr 03, 2008 at 12:32 UTC
Be aware of false strings that match. `use List::Util 'first'; my $var = '0'; if (first { $_ eq $var } $var) { print "Found.\n"; } else { print "Not found.\n"; } __END__ Not found.` [download] You could solve this by using `defined` in this particular case, but it's not a general solution. As Herkum says, `any` from List::MoreUtils is a better alternative in the general case. lodin	[reply] [d/l] [select]
Re: long if statements... What's the best way? by locked_user sundialsvc4 (Abbot) on Apr 02, 2008 at 21:53 UTC
I agree with the general sentiment that clarity and maintainability trump any (mis-guided) concerns for “efficiency.” Any Perl code that you write is going to be compiled into some kind of intermediate-format, which is what the computer actually executes. You have no control over that. What does matter, both to you and to those who'll come back from your funeral, is that the meaning of your code is abundantly clear and that it is drop-dead easy to maintain. (A good thing, since you just dropped dead. Oops.) `;-)`
Re: long if statements... What's the best way? by dragonchild (Archbishop) on Apr 02, 2008 at 18:42 UTC
Use a subroutine. My criteria for good software: Does it work? Can someone else come in, make a change, and be reasonably certain no bugs were introduced?	[reply]
Re: long if statements... What's the best way? by njweatherman (Sexton) on Apr 02, 2008 at 16:25 UTC
You can try using an if else combination. if ($var eq "a") { print "Test number one"; } elsif ($var eq "b") { print "test two"; } else { print "test three"; }	[reply]
Re^2: long if statements... What's the best way? by kyle (Abbot) on Apr 02, 2008 at 16:30 UTC
Using the double pipe ("`\|\|`") already short circuits testing. In this expression: `( $var eq 'a' \|\| $var eq 'b' \|\| $var eq 'c' )` [download] ...If it turns out that `$var eq 'a'`, the other two conditions are not checked. If `$var eq 'b'`, then only the first two conditions will be checked and not the third. Moreover, it does not appear that the OP wants to take different actions for the different values, so having separate blocks for each value found doesn't make sense.	[reply] [d/l] [select]