examples/root/exceptions2.pl

   1 #!/usr/bin/env perl
   2
   3 # This shows how Error.pm-based objects can be thrown
   4 # by Bio::Root::Root::throw() when Error.pm is available.
   5 # When Error.pm isn't available, Bio::Root::Root::throw()
   6 # works as usual.
   7 #
   8 # It also demonstrates what happens when you use an outer eval{}
   9 # instead of a try{} to trap thrown Error.pm-based exceptions.
  10 # The behavior is the same as when Error.pm is not used.
  11 # This is important for backward compatibility.
  12 #
  13 # Author: Steve Chervitz <sac@bioperl.org>
  14 #
  15 # $Id$
  16
  17 use strict;
  18
  19 use lib qw(lib/ ../../);
  20
  21 # Uncomment this line to force Bio::Root::Root::throw() to
  22 # not use Error.pm even if it's available.
  23 # Some of the tests in this script will be skipped .
  24 #BEGIN { $main::DONT_USE_ERROR = 1; }
  25
  26 use Bio::Root::Root;
  27 #use Bio::Root::Exception;  # Not necessary since Bio::Root::Root uses it.
  28 use Error qw(:try);
  29
  30 my $foo = Bio::Root::Root->new();
  31
  32 if (!$main::DONT_USE_ERROR) {
  33     try {
  34         # This is the new, fancier way to handle exceptions.
  35         # You must have Error.pm to do this (tarball included in this dir).
  36
  37         print "[1] Throwing Error within try block via call to Bio::Root::Root::throw()\n";
  38         $foo->throw( -class => 'Bio::Root::Exception',
  39                      -text  => "Oopsie!",
  40                      -value => "123"
  41                    );
  42     }
  43
  44     catch Bio::Root::Exception with {
  45         my $err = shift;
  46         print "[1] Caught Bio::Root::Exception:\n$err";
  47
  48     }
  49
  50     otherwise {
  51         my $err = shift;
  52         print "[1] Caught other Error: ", ref($err), "\n$err";
  53     };
  54
  55
  56     print "\n\n";
  57 }
  58
  59 eval {
  60
  61     # This example demonstrates the traditional method for throwing
  62     # an exception using Bio::Root::Root->throw('string').
  63     # Notice how an exception of type Bio::Root::Exception is created.
  64
  65     print "[2] Calling Bio::Root::Root->throw('string') within an eval{}\n";
  66     $foo->throw("Error message string.");
  67
  68 };
  69
  70 if($@) {
  71     print "[2] Caught eval{}-based exception: ", ref($@), "\n$@";
  72 }
  73 else {
  74     print "[2] Nothing to catch.\n";
  75 }
  76
  77
  78
  79 print "\n\n";
  80
  81 eval {
  82
  83     # This example shows that calling Error::throw directly within
  84     # an eval{} doesn't lead to a true value in $@ if
  85     # the error lacks a value.
  86
  87     print "[3] Attempting to throw a valueless Error within an eval{} block\n    (this should fail to be caught by Error.pm v0.13 but is caught by v0.14 and greater).\n";
  88
  89     if( $ENV{OSTYPE} =~ /cygwin/ ) {
  90         die "[3] This causes a segmentation fault with cygwin perl! Skipping.\n";
  91     }
  92
  93     throw Error::Simple ("A simple error.");
  94
  95 };
  96
  97 if($@) {
  98     print "[3] Caught eval{}-based exception: ", ref($@), "\n$@\n";
  99 }
 100 else {
 101     print "[3] Nothing to catch.\n";
 102 }
 103
 104
 105 print "\n\n";
 106
 107 eval {
 108
 109     # This example shows that calling Error::throw directly within
 110     # an eval{} *does* lead to a true value in $@ if the error
 111     # contains a non-zero value.
 112
 113     print "[4] Attempting to throw a valued Error within an eval{} block.\n";
 114
 115     throw Error::Simple ("A simple error.", 42);
 116
 117 };
 118
 119 if($@) {
 120     print "[4] Caught eval{}-based exception: ", ref($@), "\n$@\n";
 121 }
 122 else {
 123     print "[4] Nothing to catch.\n";
 124 }
 125
 126 print "\n\n";
 127
 128 if (!$main::DONT_USE_ERROR) {
 129     eval {
 130
 131         # This example shows what happens if we try to create a
 132         # Bio::Root::IOException (a subclass of Bio::Root::Exception)
 133         # with a zero value. Bio::Root::Exception::new() catches this
 134         # faux pas and substitutes a value that will register as true in if($@).
 135
 136         print "[5] Attempting to throw a zero-valued Bio::Root::IOException\n    within an eval{} block.\n";
 137
 138         throw Bio::Root::IOException ( -text =>"An error with zero value.",
 139                                    -value => 0);
 140
 141     };
 142
 143     if($@) {
 144         print "[5] Caught eval{}-based zero-valued exception: ", ref($@), "\n$@\n";
 145     }
 146     else {
 147         print "[5] Nothing to catch.\n";
 148     }
 149     print "\n\n";
 150 }
 151
 152
 153 eval {
 154
 155     # If Error::throw is called *indirectly* within an eval{}
 156     # (i.e., by calling a method which then calls Error::throw),
 157     # $@ is defined and it consists of a reference to the Error.pm object.
 158
 159     print "[6] Attempting to throw Error indirectly within an eval{} block \n    via Bio::Root::Root::throw()\n";
 160
 161     $foo->throw( -class => 'Bio::Root::Exception',
 162                  -text  => "Oopsie!",
 163                  -value => "456"
 164                 );
 165
 166 };
 167
 168 if($@) {
 169     print "[6] Caught eval{}-based exception: ", ref($@), "\n$@";
 170 }
 171 else {
 172     print "[6] Nothing to catch.\n";
 173 }
 174
 175 print "Done.\n";
 176
 177