1 | package UNIVERSAL; |
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2 | |
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3 | our $VERSION = '1.00'; |
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4 | |
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5 | # UNIVERSAL should not contain any extra subs/methods beyond those |
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6 | # that it exists to define. The use of Exporter below is a historical |
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7 | # accident that can't be fixed without breaking code. Note that we |
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8 | # *don't* set @ISA here, don't want all classes/objects inheriting from |
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9 | # Exporter. It's bad enough that all classes have a import() method |
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10 | # whenever UNIVERSAL.pm is loaded. |
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11 | require Exporter; |
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12 | *import = \&Exporter::import; |
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13 | @EXPORT_OK = qw(isa can VERSION); |
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14 | |
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15 | 1; |
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16 | __END__ |
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17 | |
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18 | =head1 NAME |
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19 | |
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20 | UNIVERSAL - base class for ALL classes (blessed references) |
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21 | |
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22 | =head1 SYNOPSIS |
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23 | |
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24 | $is_io = $fd->isa("IO::Handle"); |
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25 | $is_io = Class->isa("IO::Handle"); |
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26 | |
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27 | $sub = $obj->can("print"); |
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28 | $sub = Class->can("print"); |
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29 | |
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30 | use UNIVERSAL qw( isa can VERSION ); |
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31 | $yes = isa $ref, "HASH" ; |
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32 | $sub = can $ref, "fandango" ; |
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33 | $ver = VERSION $obj ; |
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34 | |
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35 | =head1 DESCRIPTION |
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36 | |
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37 | C<UNIVERSAL> is the base class which all bless references will inherit from, |
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38 | see L<perlobj>. |
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39 | |
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40 | C<UNIVERSAL> provides the following methods and functions: |
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41 | |
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42 | =over 4 |
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43 | |
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44 | =item $obj->isa( TYPE ), CLASS->isa( TYPE ), isa( VAL, TYPE ) |
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45 | |
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46 | C<TYPE> is a package name |
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47 | $obj is a blessed reference or a string containing a package name |
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48 | C<CLASS> is a package name |
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49 | C<VAL> is any of the above or an unblessed reference |
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50 | |
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51 | When used as an instance or class method (C<$obj->isa( TYPE )>), C<isa> |
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52 | returns I<true> if $obj is blessed into package C<TYPE> or inherits from |
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53 | package C<TYPE>. |
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54 | |
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55 | When used as a class method (C<CLASS->isa( TYPE )>; sometimes referred to as a |
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56 | static method), C<isa> returns I<true> if C<CLASS> inherits from (or is itself) |
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57 | the name of the package C<TYPE> or inherits from package C<TYPE>. |
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58 | |
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59 | When used as a function, like |
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60 | |
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61 | use UNIVERSAL qw( isa ) ; |
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62 | $yes = isa $h, "HASH"; |
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63 | $yes = isa "Foo", "Bar"; |
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64 | |
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65 | or |
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66 | |
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67 | require UNIVERSAL ; |
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68 | $yes = UNIVERSAL::isa $a, "ARRAY"; |
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69 | |
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70 | , C<isa> returns I<true> in the same cases as above and also if C<VAL> is an |
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71 | unblessed reference to a perl variable of type C<TYPE>, such as "HASH", |
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72 | "ARRAY", or "Regexp". |
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73 | |
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74 | =item $obj->can( METHOD ), CLASS->can( METHOD ), can( VAL, METHOD ) |
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75 | |
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76 | C<can> checks if the object or class has a method called C<METHOD>. If it does |
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77 | then a reference to the sub is returned. If it does not then I<undef> is |
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78 | returned. This includes methods inherited or imported by C<$obj>, C<CLASS>, or |
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79 | C<VAL>. |
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80 | |
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81 | C<can> cannot know whether an object will be able to provide a method |
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82 | through AUTOLOAD, so a return value of I<undef> does not necessarily mean |
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83 | the object will not be able to handle the method call. To get around |
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84 | this some module authors use a forward declaration (see L<perlsub>) |
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85 | for methods they will handle via AUTOLOAD. For such 'dummy' subs, C<can> |
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86 | will still return a code reference, which, when called, will fall through |
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87 | to the AUTOLOAD. If no suitable AUTOLOAD is provided, calling the coderef |
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88 | will cause an error. |
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89 | |
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90 | C<can> can be called as a class (static) method, an object method, or a |
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91 | function. |
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92 | |
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93 | When used as a function, if C<VAL> is a blessed reference or package name which |
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94 | has a method called C<METHOD>, C<can> returns a reference to the subroutine. |
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95 | If C<VAL> is not a blessed reference, or if it does not have a method |
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96 | C<METHOD>, I<undef> is returned. |
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97 | |
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98 | =item VERSION ( [ REQUIRE ] ) |
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99 | |
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100 | C<VERSION> will return the value of the variable C<$VERSION> in the |
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101 | package the object is blessed into. If C<REQUIRE> is given then |
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102 | it will do a comparison and die if the package version is not |
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103 | greater than or equal to C<REQUIRE>. |
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104 | |
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105 | C<VERSION> can be called as either a class (static) method, an object method or |
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106 | or a function. |
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107 | |
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108 | |
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109 | =back |
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110 | |
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111 | These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>. |
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112 | If you want simple local access to them you can do |
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113 | |
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114 | *isa = \&UNIVERSAL::isa; |
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115 | |
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116 | to import isa into your package. |
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117 | |
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118 | =cut |
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