((Conditional, Ternary Operator)) Specifying default and non-default values

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

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Re: Conditional, Ternary Operator - Specifying default and non-default values by ncw (Friar) on Oct 02, 2000 at 22:42 UTC
This script nicely demonstrates a bad use of map - if you are discarding the output of map then you should use for/foreach. You can tidy the ternary operator up too. I'd write something like (untested but optimised for brevity :-) `$extension{index} = 'pod'; system "pod2html $_." . ($extension{$_} \|\| 'pm') . " > $_.html" for (qw(HostCycle Instinet index));` [download] For real I'd put an or die after the system though ;-) Update: I did test it, and I got this result $ perl - [fx: cuts and pastes the code above] Can't open HostCycle.pm: No such file or directory Can't open Instinet.pm: No such file or directory Can't open index.pod: No such file or directory It works! (The error messages are from pod2html.)	[reply] [d/l]
(tye)Re: ((Conditional, Ternary Operator)) Specifying default and non-default by tye (Sage) on Oct 02, 2000 at 22:49 UTC
If you already have the very useful `def` in your toolbag: `sub def { $_[0]= def($_[1],"") if ! defined $_[0]; return $_[0]; }` [download] then you can do this as: `$ext{index} = 'pod'; for my $pod ( qw( HostCycle Instinet index ) ) { system "pod2html $pod" . def($ext{$pod},".pm") . " > $pod.html"; }` [download] `def` (short for "define" which would be too easy to confuse with "defined") is useful for avoiding warnings. You can use it like `\|\|` as above or like `\|\|=`. It differs from these two operators in that it triggers on definedness rather than truthness. Note that `def` is so useful that even `def` uses it. ;) - tye (but my friends call me "Tye")	[reply] [d/l] [select]
Re: ((Conditional by cwest (Friar) on Oct 02, 2000 at 23:43 UTC
`my @pod = qw(HostCycle Instinet index); my %ext = ( index => 'pod' ); system "pod2html $_.".($ext{$_}?$ext{$_}:'pm')." > $_.html" foreach @p +od;` [download] Enjoy! -- Casey I am a superhero.	[reply] [d/l]
Re: ((Conditional by runrig (Abbot) on Oct 02, 2000 at 22:51 UTC
Map in void context - bad. just use a for loop: `@pod = qw(HostCycle Instinet index); $extension{index} = '.pod'; for (@pod) { # Assuming there's no '0' or blank extensions $infile_extension = $extension{$_} \|\| '.pm'; # Otherwise use this #$infile_extension = exists $extension{$_} ? $extension{$_} : '.pm'; # Check status ? system "pod2html $_$infile_extension > $_.html" and die "pod2html fai +led: $!"; }` [download] I've just made it longer, oh well...	[reply] [d/l]