my $coderef = \&hiya; is far more conventional, but both are ok for subroutines.

Neither will work for operators such as gmtime and localtime, though.

Since 5.16:

my $time_zone_func =
   $file =~ /^London/
      ? \&CORE::gmtime
      : \&CORE::localtime;

strftime($date_format, $time_zone_func->(time))
[download]

Backwards compatible:

my $time_zone_func =
   $file =~ /^London/
      ? sub { gmtime($_[0]) }
      : sub { localtime($_[0]) };

strftime($date_format, $time_zone_func->(time))
[download]

or

my $time_zone_func = sub {
   $file =~ /^London/
      ? gmtime($_[0])
      : localtime($_[0])
};

strftime($date_format, $time_zone_func->(time))
[download]