Question

I was wondering if anyone had any suggestions on improving the following code (if possible) so that it didn’t need the repeated (my @a = $time =~ …), possibly using case/switch or given/when or some other idea that i’m missing?

my $time = '12:59pm';

if( my @a = $time =~ m/^(\d\d?)(am|pm)$/ )        { tell_time( $a[0], 0, $a[1] ) }
if( my @a = $time =~ m/^(\d\d?):(\d\d)(am|pm)$/ ) { tell_time( @a ) }
if( my @a = $time =~ m/^(\d\d?):(\d\d)$/ )        { tell_time( @a ) }

sub tell_time
{
    my $hour    = shift;
    my $minute  = shift || '00';
    my $ampm    = shift || ( $hour > 12 ) ? 'pm' : 'am';

    print "Hour: $hour, Minute: $minute, AMPM: $ampm\n";
}

I’ve tried playing around with Switch and the 5.10 given/when but can’t seem to be able to do something like:

given( $time )
{
    when( /^(\d\d?)(am|pm)$/ )        { tell_time( $_[0], 0, $_[1] ) }
    when( /^(\d\d?):(\d\d)(am|pm)$/ ) { tell_time( @_ ) }
    when( /^(\d\d?):(\d\d)$/ )        { tell_time( @_ ) }
}

That doesn’t fly because @_ appears to be storing $time.

also note I’m more interested in the syntax of the problem than the problem the code solves. I’m well aware that I could use Time::ParseDate to figure out the various parts of a string formatted like a time or date.

Answer 1

Your regex uses () to extract matches, but you don’t have to store these in an array. If you want, they’re stored in $1, $2, $3, and so on. Lookie:

given( $time )
{
    when( /^(\d\d?)(am|pm)$/ )        { tell_time( $1, 0, $2 ) }
    when( /^(\d\d?):(\d\d)(am|pm)$/ ) { tell_time( $1, $2, $3 ) }
    when( /^(\d\d?):(\d\d)$/ )        { tell_time( $1, $2 ) }
}

Does exactly what I think you want to do.

If you want to add to the syntax, I would write tell_time() to simply take the time as a string, and have the function parse the result itself, rather than make the user of your code parse it himself. Alternatively, you could use this given() block as the start of a new function that does exactly that – parses a time string and passes it correctly to tell_time(). But that’s just me. I don’t know what you need your code to do, so by all means go for it.