SGI Freeware 1999 August/SGI Freeware 1999 August.iso/dist/fw_perl.idb/usr/freeware/catman/p_man/cat3/Class::Struct.Z/Class::Struct

Text File | 1998-10-28 | 12.0 KB | 397 lines

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     NNNNAAAAMMMMEEEE
      Class::Struct    - declare struct-like datatypes    as Perl
      classes

     SSSSYYYYNNNNOOOOPPPPSSSSIIIISSSS
          use Class::Struct;
              #    declare    struct,    based on array:
          struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ...    ]);
              #    declare    struct,    based on hash:
          struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ...    });

          package CLASS_NAME;
          use Class::Struct;
              #    declare    struct,    based on array,    implicit class name:
          struct( ELEMENT_NAME => ELEMENT_TYPE, ...    );

          package Myobj;
          use Class::Struct;
              #    declare    struct with four types of elements:
          struct( s    => '$',    a => '@', h => '%', c => 'My_Other_Class' );

          $obj = new Myobj;              #    constructor

                          #    scalar type accessor:
          $element_value = $obj->s;          # element value
          $obj->s('new value');          # assign to element

                          #    array type accessor:
          $ary_ref = $obj->a;          # reference to whole array
          $ary_element_value = $obj->a(2);      # array element value
          $obj->a(2, 'new value');          # assign to array element

                          #    hash type accessor:
          $hash_ref    = $obj->h;          # reference to whole hash
          $hash_element_value = $obj->h('x'); # hash element value
          $obj->h('x', 'new    value');    # assign to hash element

                          #    class type accessor:
          $element_value = $obj->c;          # object reference
          $obj->c->method(...);          # call method    of object
          $obj->c(new My_Other_Class);      # assign a new object


     DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
      Class::Struct    exports    a single function, struct.  Given a
      list of element names    and types, and optionally a class
      name,    struct creates a Perl 5    class that implements a
      "struct-like"    data structure.

      The new class    is given a constructor method, new, for
      creating struct objects.




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      Each element in the struct data has an accessor method,
      which    is used    to assign to the element and to    fetch its
      value.  The default accessor can be overridden by declaring
      a sub    of the same name in the    package.  (See Example 2.)

      Each element's type can be scalar, array, hash, or class.

      TTTThhhheeee ssssttttrrrruuuucccctttt(((()))) function

      The struct function has three    forms of parameter-list.

          struct( CLASS_NAME => [ ELEMENT_LIST ]);
          struct( CLASS_NAME => { ELEMENT_LIST });
          struct( ELEMENT_LIST );

      The first and    second forms explicitly    identify the name of
      the class being created.  The    third form assumes the current
      package name as the class name.

      An object of a class created by the first and    third forms is
      based    on an array, whereas an    object of a class created by
      the second form is based on a    hash. The array-based forms
      will be somewhat faster and smaller; the hash-based forms
      are more flexible.

      The class created by struct must not be a subclass of
      another class    other than UNIVERSAL.

      A function named new must not    be explicitly defined in a
      class    created    by struct.

      The _E_L_E_M_E_N_T__L_I_S_T has the form

          NAME => TYPE, ...

      Each name-type pair declares one element of the struct. Each
      element name will be defined as an accessor method unless a
      method by that name is explicitly defined; in    the latter
      case,    a warning is issued if the warning flag    (----wwww) is    set.

      EEEElllleeeemmmmeeeennnntttt TTTTyyyyppppeeeessss    aaaannnndddd AAAAcccccccceeeessssssssoooorrrr MMMMeeeetttthhhhooooddddssss

      The four element types -- scalar, array, hash, and class --
      are represented by strings --    '$', '@', '%', and a class
      name -- optionally preceded by a '*'.

      The accessor method provided by struct for an    element
      depends on the declared type of the element.

      Scalar ('$' or '*$')
           The element is a    scalar,    and is initialized to undef.




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           The accessor's argument,    if any,    is assigned to the
           element.

           If the element type is '$', the value of    the element
           (after assignment) is returned. If the element type is
           '*$', a reference to the    element    is returned.

      Array    ('@' or    '*@')
           The element is an array,    initialized to ().

           With no argument, the accessor returns a    reference to
           the element's whole array.

           With one    or two arguments, the first argument is    an
           index specifying    one element of the array; the second
           argument, if present, is    assigned to the    array element.
           If the element type is '@', the accessor    returns    the
           array element value.  If    the element type is '*@', a
           reference to the    array element is returned.

      Hash ('%' or '*%')
           The element is a    hash, initialized to ().

           With no argument, the accessor returns a    reference to
           the element's whole hash.

           With one    or two arguments, the first argument is    a key
           specifying one element of the hash; the second
           argument, if present, is    assigned to the    hash element.
           If the element type is '%', the accessor    returns    the
           hash element value.  If the element type    is '*%', a
           reference to the    hash element is    returned.

      Class    ('Class_Name' or '*Class_Name')
           The element's value must    be a reference blessed to the
           named class or to one of    its subclasses.    The element is
           initialized to the result of calling the    new
           constructor of the named    class.

           The accessor's argument,    if any,    is assigned to the
           element.    The accessor will croak    if this    is not an
           appropriate object reference.

           If the element type does    not start with a '*', the
           accessor    returns    the element value (after assignment).
           If the element type starts with a '*', a    reference to
           the element itself is returned.

     EEEEXXXXAAAAMMMMPPPPLLLLEEEESSSS
      Example 1
           Giving a    struct element a class type that is also a
           struct is how structs are nested.  Here,    timeval



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           represents a time (seconds and microseconds), and
           rusage has two elements,    each of    which is of type
           timeval.

           use Class::Struct;

           struct( rusage => {
               ru_utime    => timeval,  # seconds
               ru_stime    => timeval,  # microseconds
           });

           struct( timeval => [
               tv_secs    => '$',
               tv_usecs    => '$',
           ]);

               # create    an object:
           my $t = new rusage;
               # $t->ru_utime and $t->ru_stime are objects of type timeval.

               # set $t->ru_utime to 100.0 sec and $t->ru_stime    to 5.0 sec.
           $t->ru_utime->tv_secs(100);
           $t->ru_utime->tv_usecs(0);
           $t->ru_stime->tv_secs(5);
           $t->ru_stime->tv_usecs(0);


      Example 2
           An accessor function can    be redefined in    order to
           provide additional checking of values, etc.  Here, we
           want the    count element always to    be nonnegative,    so we
           redefine    the count accessor accordingly.

           package MyObj;
           use Class::Struct;

                   # declare the struct
           struct ( 'MyObj', { count =>    '$', stuff => '%' } );

                   # override the default accessor method for 'count'
           sub count {
               my $self    = shift;
               if ( @_ ) {
               die 'count must be nonnegative' if $_[0] < 0;
               $self->{'count'} = shift;
               warn    "Too many args to count" if @_;
               }
               return $self->{'count'};
           }






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           package main;
           $x =    new MyObj;
           print "\$x->count(5)    = ", $x->count(5), "\n";
                       # prints '$x->count(5) = 5'

           print "\$x->count = ", $x->count, "\n";
                       # prints '$x->count = 5'

           print "\$x->count(-5) = ", $x->count(-5), "\n";
                       # dies due to negative argument!


     AAAAuuuutttthhhhoooorrrr aaaannnndddd    MMMMooooddddiiiiffffiiiiccccaaaattttiiiioooonnnn HHHHiiiissssttttoooorrrryyyy
      Renamed to Class::Struct and modified    by Jim Miner, 1997-
      04-02.

          members()    function removed.
          Documentation corrected and extended.
          Use of struct() in a subclass prohibited.
          User definition of accessor allowed.
          Treatment    of '*' in element types    corrected.
          Treatment    of classes as element types corrected.
          Class name to struct() made optional.
          Diagnostic checks    added.

      Originally Class::Template by    Dean Roehrich.

          #    Template.pm   --- struct/member    template builder
          #      12mar95
          #      Dean Roehrich
          #
          #    changes/bugs fixed since 28nov94 version:
          #     - podified
          #    changes/bugs fixed since 21nov94 version:
          #     - Fixed examples.
          #    changes/bugs fixed since 02sep94 version:
          #     - Moved to Class::Template.
          #    changes/bugs fixed since 20feb94 version:
          #     - Updated to be a more    proper module.
          #     - Added "use strict".
          #     - Bug in build_methods, was using @var    when @$var needed.
          #     - Now using my() rather than local().
          #
          #    Uses perl5 classes to create nested data types.
          #    This is    offered    as one implementation of Tom Christiansen's "structs.pl"
          #    idea.









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