1 | package UNIVERSAL; |
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2 | |
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3 | # UNIVERSAL should not contain any extra subs/methods beyond those |
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4 | # that it exists to define. The use of Exporter below is a historical |
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5 | # accident that should be fixed sometime. |
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6 | require Exporter; |
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7 | *import = \&Exporter::import; |
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8 | @EXPORT_OK = qw(isa can); |
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9 | |
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10 | 1; |
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11 | __END__ |
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12 | |
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13 | =head1 NAME |
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14 | |
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15 | UNIVERSAL - base class for ALL classes (blessed references) |
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16 | |
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17 | =head1 SYNOPSIS |
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18 | |
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19 | $io = $fd->isa("IO::Handle"); |
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20 | $sub = $obj->can('print'); |
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21 | |
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22 | $yes = UNIVERSAL::isa($ref, "HASH"); |
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23 | |
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24 | =head1 DESCRIPTION |
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25 | |
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26 | C<UNIVERSAL> is the base class which all bless references will inherit from, |
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27 | see L<perlobj> |
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28 | |
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29 | C<UNIVERSAL> provides the following methods |
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30 | |
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31 | =over 4 |
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32 | |
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33 | =item isa ( TYPE ) |
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34 | |
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35 | C<isa> returns I<true> if C<REF> is blessed into package C<TYPE> |
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36 | or inherits from package C<TYPE>. |
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37 | |
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38 | C<isa> can be called as either a static or object method call. |
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39 | |
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40 | =item can ( METHOD ) |
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41 | |
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42 | C<can> checks if the object has a method called C<METHOD>. If it does |
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43 | then a reference to the sub is returned. If it does not then I<undef> |
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44 | is returned. |
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45 | |
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46 | C<can> can be called as either a static or object method call. |
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47 | |
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48 | =item VERSION ( [ REQUIRE ] ) |
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49 | |
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50 | C<VERSION> will return the value of the variable C<$VERSION> in the |
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51 | package the object is blessed into. If C<REQUIRE> is given then |
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52 | it will do a comparison and die if the package version is not |
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53 | greater than or equal to C<REQUIRE>. |
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54 | |
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55 | C<VERSION> can be called as either a static or object method call. |
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56 | |
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57 | =back |
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58 | |
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59 | The C<isa> and C<can> methods can also be called as subroutines |
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60 | |
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61 | =over 4 |
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62 | |
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63 | =item UNIVERSAL::isa ( VAL, TYPE ) |
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64 | |
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65 | C<isa> returns I<true> if one of the following statements is true. |
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66 | |
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67 | =over 8 |
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68 | |
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69 | =item * |
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70 | |
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71 | C<VAL> is a reference blessed into either package C<TYPE> or a package |
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72 | which inherits from package C<TYPE>. |
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73 | |
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74 | =item * |
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75 | |
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76 | C<VAL> is a reference to a C<TYPE> of Perl variable (e.g. 'HASH'). |
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77 | |
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78 | =item * |
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79 | |
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80 | C<VAL> is the name of a package that inherits from (or is itself) |
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81 | package C<TYPE>. |
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82 | |
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83 | =back |
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84 | |
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85 | =item UNIVERSAL::can ( VAL, METHOD ) |
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86 | |
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87 | If C<VAL> is a blessed reference which has a method called C<METHOD>, |
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88 | C<can> returns a reference to the subroutine. If C<VAL> is not |
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89 | a blessed reference, or if it does not have a method C<METHOD>, |
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90 | I<undef> is returned. |
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91 | |
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92 | =back |
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93 | |
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94 | These subroutines should I<not> be imported via S<C<use UNIVERSAL qw(...)>>. |
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95 | If you want simple local access to them you can do |
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96 | |
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97 | *isa = \&UNIVERSAL::isa; |
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98 | |
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99 | to import isa into your package. |
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100 | |
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101 | =cut |
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