mingw/html/lib/Class/Struct.html

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  13 <big><strong><span class="block">&nbsp;Class::Struct - declare struct-like datatypes as Perl classes</span></strong></big>
  14 </td></tr>
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  16
  17 <p><a name="__index__"></a></p>
  18 <!-- INDEX BEGIN -->
  19
  20 <ul>
  21
  22         <li><a href="#name">NAME</a></li>
  23         <li><a href="#synopsis">SYNOPSIS</a></li>
  24         <li><a href="#description">DESCRIPTION</a></li>
  25         <ul>
  26
  27                 <li><a href="#the_struct___function">The <code>struct()</code> function</a></li>
  28                 <li><a href="#class_creation_at_compile_time">Class Creation at Compile Time</a></li>
  29                 <li><a href="#element_types_and_accessor_methods">Element Types and Accessor Methods</a></li>
  30                 <li><a href="#initializing_with_new">Initializing with <code>new</code></a></li>
  31         </ul>
  32
  33         <li><a href="#examples">EXAMPLES</a></li>
  34         <li><a href="#author_and_modification_history">Author and Modification History</a></li>
  35 </ul>
  36 <!-- INDEX END -->
  37
  38 <hr />
  39 <p>
  40 </p>
  41 <h1><a name="name">NAME</a></h1>
  42 <p>Class::Struct - declare struct-like datatypes as Perl classes</p>
  43 <p>
  44 </p>
  45 <hr />
  46 <h1><a name="synopsis">SYNOPSIS</a></h1>
  47 <pre>
  48     use Class::Struct;
  49             # declare struct, based on array:
  50     struct( CLASS_NAME =&gt; [ ELEMENT_NAME =&gt; ELEMENT_TYPE, ... ]);
  51             # declare struct, based on hash:
  52     struct( CLASS_NAME =&gt; { ELEMENT_NAME =&gt; ELEMENT_TYPE, ... });</pre>
  53 <pre>
  54     package CLASS_NAME;
  55     use Class::Struct;
  56             # declare struct, based on array, implicit class name:
  57     struct( ELEMENT_NAME =&gt; ELEMENT_TYPE, ... );</pre>
  58 <pre>
  59     # Declare struct at compile time
  60     use Class::Struct CLASS_NAME =&gt; [ ELEMENT_NAME =&gt; ELEMENT_TYPE, ... ];
  61     use Class::Struct CLASS_NAME =&gt; { ELEMENT_NAME =&gt; ELEMENT_TYPE, ... };</pre>
  62 <pre>
  63     # declare struct at compile time, based on array, implicit class name:
  64     package CLASS_NAME;
  65     use Class::Struct ELEMENT_NAME =&gt; ELEMENT_TYPE, ... ;</pre>
  66 <pre>
  67     package Myobj;
  68     use Class::Struct;
  69             # declare struct with four types of elements:
  70     struct( s =&gt; '$', a =&gt; '@', h =&gt; '%', c =&gt; 'My_Other_Class' );</pre>
  71 <pre>
  72     $obj = new Myobj;               # constructor</pre>
  73 <pre>
  74                                     # scalar type accessor:
  75     $element_value = $obj-&gt;s;           # element value
  76     $obj-&gt;s('new value');               # assign to element</pre>
  77 <pre>
  78                                     # array type accessor:
  79     $ary_ref = $obj-&gt;a;                 # reference to whole array
  80     $ary_element_value = $obj-&gt;a(2);    # array element value
  81     $obj-&gt;a(2, 'new value');            # assign to array element</pre>
  82 <pre>
  83                                     # hash type accessor:
  84     $hash_ref = $obj-&gt;h;                # reference to whole hash
  85     $hash_element_value = $obj-&gt;h('x'); # hash element value
  86     $obj-&gt;h('x', 'new value');          # assign to hash element</pre>
  87 <pre>
  88                                     # class type accessor:
  89     $element_value = $obj-&gt;c;           # object reference
  90     $obj-&gt;c-&gt;method(...);               # call method of object
  91     $obj-&gt;c(new My_Other_Class);        # assign a new object</pre>
  92 <p>
  93 </p>
  94 <hr />
  95 <h1><a name="description">DESCRIPTION</a></h1>
  96 <p><code>Class::Struct</code> exports a single function, <code>struct</code>.
  97 Given a list of element names and types, and optionally
  98 a class name, <code>struct</code> creates a Perl 5 class that implements
  99 a ``struct-like'' data structure.</p>
 100 <p>The new class is given a constructor method, <code>new</code>, for creating
 101 struct objects.</p>
 102 <p>Each element in the struct data has an accessor method, which is
 103 used to assign to the element and to fetch its value.  The
 104 default accessor can be overridden by declaring a <code>sub</code> of the
 105 same name in the package.  (See Example 2.)</p>
 106 <p>Each element's type can be scalar, array, hash, or class.</p>
 107 <p>
 108 </p>
 109 <h2><a name="the_struct___function">The <code>struct()</code> function</a></h2>
 110 <p>The <code>struct</code> function has three forms of parameter-list.</p>
 111 <pre>
 112     struct( CLASS_NAME =&gt; [ ELEMENT_LIST ]);
 113     struct( CLASS_NAME =&gt; { ELEMENT_LIST });
 114     struct( ELEMENT_LIST );</pre>
 115 <p>The first and second forms explicitly identify the name of the
 116 class being created.  The third form assumes the current package
 117 name as the class name.</p>
 118 <p>An object of a class created by the first and third forms is
 119 based on an array, whereas an object of a class created by the
 120 second form is based on a hash. The array-based forms will be
 121 somewhat faster and smaller; the hash-based forms are more
 122 flexible.</p>
 123 <p>The class created by <code>struct</code> must not be a subclass of another
 124 class other than <code>UNIVERSAL</code>.</p>
 125 <p>It can, however, be used as a superclass for other classes. To facilitate
 126 this, the generated constructor method uses a two-argument blessing.
 127 Furthermore, if the class is hash-based, the key of each element is
 128 prefixed with the class name (see <em>Perl Cookbook</em>, Recipe 13.12).</p>
 129 <p>A function named <code>new</code> must not be explicitly defined in a class
 130 created by <code>struct</code>.</p>
 131 <p>The <em>ELEMENT_LIST</em> has the form</p>
 132 <pre>
 133     NAME =&gt; TYPE, ...</pre>
 134 <p>Each name-type pair declares one element of the struct. Each
 135 element name will be defined as an accessor method unless a
 136 method by that name is explicitly defined; in the latter case, a
 137 warning is issued if the warning flag (<strong>-w</strong>) is set.</p>
 138 <p>
 139 </p>
 140 <h2><a name="class_creation_at_compile_time">Class Creation at Compile Time</a></h2>
 141 <p><code>Class::Struct</code> can create your class at compile time.  The main reason
 142 for doing this is obvious, so your class acts like every other class in
 143 Perl.  Creating your class at compile time will make the order of events
 144 similar to using any other class ( or Perl module ).</p>
 145 <p>There is no significant speed gain between compile time and run time
 146 class creation, there is just a new, more standard order of events.</p>
 147 <p>
 148 </p>
 149 <h2><a name="element_types_and_accessor_methods">Element Types and Accessor Methods</a></h2>
 150 <p>The four element types -- scalar, array, hash, and class -- are
 151 represented by strings -- <code>'$'</code>, <code>'@'</code>, <code>'%'</code>, and a class name --
 152 optionally preceded by a <code>'*'</code>.</p>
 153 <p>The accessor method provided by <code>struct</code> for an element depends
 154 on the declared type of the element.</p>
 155 <dl>
 156 <dt><strong><a name="item_scalar">Scalar (<code>'$'</code> or <code>'*$'</code>)</a></strong>
 157
 158 <dd>
 159 <p>The element is a scalar, and by default is initialized to <a href="file://C|\msysgit\mingw\html/pod/perlfunc.html#item_undef"><code>undef</code></a>
 160 (but see <a href="#initializing_with_new">Initializing with new</a>).</p>
 161 </dd>
 162 <dd>
 163 <p>The accessor's argument, if any, is assigned to the element.</p>
 164 </dd>
 165 <dd>
 166 <p>If the element type is <code>'$'</code>, the value of the element (after
 167 assignment) is returned. If the element type is <code>'*$'</code>, a reference
 168 to the element is returned.</p>
 169 </dd>
 170 </li>
 171 <dt><strong><a name="item_array">Array (<code>'@'</code> or <code>'*@'</code>)</a></strong>
 172
 173 <dd>
 174 <p>The element is an array, initialized by default to <code>()</code>.</p>
 175 </dd>
 176 <dd>
 177 <p>With no argument, the accessor returns a reference to the
 178 element's whole array (whether or not the element was
 179 specified as <code>'@'</code> or <code>'*@'</code>).</p>
 180 </dd>
 181 <dd>
 182 <p>With one or two arguments, the first argument is an index
 183 specifying one element of the array; the second argument, if
 184 present, is assigned to the array element.  If the element type
 185 is <code>'@'</code>, the accessor returns the array element value.  If the
 186 element type is <code>'*@'</code>, a reference to the array element is
 187 returned.</p>
 188 </dd>
 189 <dd>
 190 <p>As a special case, when the accessor is called with an array reference
 191 as the sole argument, this causes an assignment of the whole array element.
 192 The object reference is returned.</p>
 193 </dd>
 194 </li>
 195 <dt><strong><a name="item_hash">Hash (<code>'%'</code> or <code>'*%'</code>)</a></strong>
 196
 197 <dd>
 198 <p>The element is a hash, initialized by default to <code>()</code>.</p>
 199 </dd>
 200 <dd>
 201 <p>With no argument, the accessor returns a reference to the
 202 element's whole hash (whether or not the element was
 203 specified as <code>'%'</code> or <code>'*%'</code>).</p>
 204 </dd>
 205 <dd>
 206 <p>With one or two arguments, the first argument is a key specifying
 207 one element of the hash; the second argument, if present, is
 208 assigned to the hash element.  If the element type is <code>'%'</code>, the
 209 accessor returns the hash element value.  If the element type is
 210 <code>'*%'</code>, a reference to the hash element is returned.</p>
 211 </dd>
 212 <dd>
 213 <p>As a special case, when the accessor is called with a hash reference
 214 as the sole argument, this causes an assignment of the whole hash element.
 215 The object reference is returned.</p>
 216 </dd>
 217 </li>
 218 <dt><strong><a name="item_class">Class (<code>'Class_Name'</code> or <code>'*Class_Name'</code>)</a></strong>
 219
 220 <dd>
 221 <p>The element's value must be a reference blessed to the named
 222 class or to one of its subclasses. The element is not initialized
 223 by default.</p>
 224 </dd>
 225 <dd>
 226 <p>The accessor's argument, if any, is assigned to the element. The
 227 accessor will <code>croak</code> if this is not an appropriate object
 228 reference.</p>
 229 </dd>
 230 <dd>
 231 <p>If the element type does not start with a <code>'*'</code>, the accessor
 232 returns the element value (after assignment). If the element type
 233 starts with a <code>'*'</code>, a reference to the element itself is returned.</p>
 234 </dd>
 235 </li>
 236 </dl>
 237 <p>
 238 </p>
 239 <h2><a name="initializing_with_new">Initializing with <code>new</code></a></h2>
 240 <p><code>struct</code> always creates a constructor called <code>new</code>. That constructor
 241 may take a list of initializers for the various elements of the new
 242 struct.</p>
 243 <p>Each initializer is a pair of values: <em>element name</em><code> =&gt; </code><em>value</em>.
 244 The initializer value for a scalar element is just a scalar value. The
 245 initializer for an array element is an array reference. The initializer
 246 for a hash is a hash reference.</p>
 247 <p>The initializer for a class element is an object of the corresponding class,
 248 or of one of it's subclasses, or a reference to a hash containing named
 249 arguments to be passed to the element's constructor.</p>
 250 <p>See Example 3 below for an example of initialization.</p>
 251 <p>
 252 </p>
 253 <hr />
 254 <h1><a name="examples">EXAMPLES</a></h1>
 255 <dl>
 256 <dt><strong><a name="item_example_1">Example 1</a></strong>
 257
 258 <dd>
 259 <p>Giving a struct element a class type that is also a struct is how
 260 structs are nested.  Here, <code>Timeval</code> represents a time (seconds and
 261 microseconds), and <code>Rusage</code> has two elements, each of which is of
 262 type <code>Timeval</code>.</p>
 263 </dd>
 264 <dd>
 265 <pre>
 266     use Class::Struct;</pre>
 267 </dd>
 268 <dd>
 269 <pre>
 270     struct( Rusage =&gt; {
 271         ru_utime =&gt; 'Timeval',  # user time used
 272         ru_stime =&gt; 'Timeval',  # system time used
 273     });</pre>
 274 </dd>
 275 <dd>
 276 <pre>
 277     struct( Timeval =&gt; [
 278         tv_secs  =&gt; '$',        # seconds
 279         tv_usecs =&gt; '$',        # microseconds
 280     ]);</pre>
 281 </dd>
 282 <dd>
 283 <pre>
 284         # create an object:
 285     my $t = Rusage-&gt;new(ru_utime=&gt;Timeval-&gt;new(), ru_stime=&gt;Timeval-&gt;new());</pre>
 286 </dd>
 287 <dd>
 288 <pre>
 289         # $t-&gt;ru_utime and $t-&gt;ru_stime are objects of type Timeval.
 290         # set $t-&gt;ru_utime to 100.0 sec and $t-&gt;ru_stime to 5.0 sec.
 291     $t-&gt;ru_utime-&gt;tv_secs(100);
 292     $t-&gt;ru_utime-&gt;tv_usecs(0);
 293     $t-&gt;ru_stime-&gt;tv_secs(5);
 294     $t-&gt;ru_stime-&gt;tv_usecs(0);</pre>
 295 </dd>
 296 </li>
 297 <dt><strong><a name="item_example_2">Example 2</a></strong>
 298
 299 <dd>
 300 <p>An accessor function can be redefined in order to provide
 301 additional checking of values, etc.  Here, we want the <code>count</code>
 302 element always to be nonnegative, so we redefine the <code>count</code>
 303 accessor accordingly.</p>
 304 </dd>
 305 <dd>
 306 <pre>
 307     package MyObj;
 308     use Class::Struct;</pre>
 309 </dd>
 310 <dd>
 311 <pre>
 312     # declare the struct
 313     struct ( 'MyObj', { count =&gt; '$', stuff =&gt; '%' } );</pre>
 314 </dd>
 315 <dd>
 316 <pre>
 317     # override the default accessor method for 'count'
 318     sub count {
 319         my $self = shift;
 320         if ( @_ ) {
 321             die 'count must be nonnegative' if $_[0] &lt; 0;
 322             $self-&gt;{'MyObj::count'} = shift;
 323             warn &quot;Too many args to count&quot; if @_;
 324         }
 325         return $self-&gt;{'MyObj::count'};
 326     }</pre>
 327 </dd>
 328 <dd>
 329 <pre>
 330     package main;
 331     $x = new MyObj;
 332     print &quot;\$x-&gt;count(5) = &quot;, $x-&gt;count(5), &quot;\n&quot;;
 333                             # prints '$x-&gt;count(5) = 5'</pre>
 334 </dd>
 335 <dd>
 336 <pre>
 337     print &quot;\$x-&gt;count = &quot;, $x-&gt;count, &quot;\n&quot;;
 338                             # prints '$x-&gt;count = 5'</pre>
 339 </dd>
 340 <dd>
 341 <pre>
 342     print &quot;\$x-&gt;count(-5) = &quot;, $x-&gt;count(-5), &quot;\n&quot;;
 343                             # dies due to negative argument!</pre>
 344 </dd>
 345 </li>
 346 <dt><strong><a name="item_example_3">Example 3</a></strong>
 347
 348 <dd>
 349 <p>The constructor of a generated class can be passed a list
 350 of <em>element</em>=&gt;<em>value</em> pairs, with which to initialize the struct.
 351 If no initializer is specified for a particular element, its default
 352 initialization is performed instead. Initializers for non-existent
 353 elements are silently ignored.</p>
 354 </dd>
 355 <dd>
 356 <p>Note that the initializer for a nested class may be specified as
 357 an object of that class, or as a reference to a hash of initializers
 358 that are passed on to the nested struct's constructor.</p>
 359 </dd>
 360 <dd>
 361 <pre>
 362     use Class::Struct;</pre>
 363 </dd>
 364 <dd>
 365 <pre>
 366     struct Breed =&gt;
 367     {
 368         name  =&gt; '$',
 369         cross =&gt; '$',
 370     };</pre>
 371 </dd>
 372 <dd>
 373 <pre>
 374     struct Cat =&gt;
 375     [
 376         name     =&gt; '$',
 377         kittens  =&gt; '@',
 378         markings =&gt; '%',
 379         breed    =&gt; 'Breed',
 380     ];</pre>
 381 </dd>
 382 <dd>
 383 <pre>
 384     my $cat = Cat-&gt;new( name     =&gt; 'Socks',
 385                         kittens  =&gt; ['Monica', 'Kenneth'],
 386                         markings =&gt; { socks=&gt;1, blaze=&gt;&quot;white&quot; },
 387                         breed    =&gt; Breed-&gt;new(name=&gt;'short-hair', cross=&gt;1),
 388                    or:  breed    =&gt; {name=&gt;'short-hair', cross=&gt;1},
 389                       );</pre>
 390 </dd>
 391 <dd>
 392 <pre>
 393     print &quot;Once a cat called &quot;, $cat-&gt;name, &quot;\n&quot;;
 394     print &quot;(which was a &quot;, $cat-&gt;breed-&gt;name, &quot;)\n&quot;;
 395     print &quot;had two kittens: &quot;, join(' and ', @{$cat-&gt;kittens}), &quot;\n&quot;;</pre>
 396 </dd>
 397 </li>
 398 </dl>
 399 <p>
 400 </p>
 401 <hr />
 402 <h1><a name="author_and_modification_history">Author and Modification History</a></h1>
 403 <p>Modified by Damian Conway, 2001-09-10, v0.62.</p>
 404 <pre>
 405    Modified implicit construction of nested objects.
 406    Now will also take an object ref instead of requiring a hash ref.
 407    Also default initializes nested object attributes to undef, rather
 408    than calling object constructor without args
 409    Original over-helpfulness was fraught with problems:
 410        * the class's constructor might not be called 'new'
 411        * the class might not have a hash-like-arguments constructor
 412        * the class might not have a no-argument constructor
 413        * &quot;recursive&quot; data structures didn't work well:
 414                  package Person;
 415                  struct { mother =&gt; 'Person', father =&gt; 'Person'};</pre>
 416 <p>Modified by Casey West, 2000-11-08, v0.59.</p>
 417 <pre>
 418     Added the ability for compile time class creation.</pre>
 419 <p>Modified by Damian Conway, 1999-03-05, v0.58.</p>
 420 <pre>
 421     Added handling of hash-like arg list to class ctor.</pre>
 422 <pre>
 423     Changed to two-argument blessing in ctor to support
 424     derivation from created classes.</pre>
 425 <pre>
 426     Added classname prefixes to keys in hash-based classes
 427     (refer to &quot;Perl Cookbook&quot;, Recipe 13.12 for rationale).</pre>
 428 <pre>
 429     Corrected behaviour of accessors for '*@' and '*%' struct
 430     elements.  Package now implements documented behaviour when
 431     returning a reference to an entire hash or array element.
 432     Previously these were returned as a reference to a reference
 433     to the element.</pre>
 434 <p>Renamed to <code>Class::Struct</code> and modified by Jim Miner, 1997-04-02.</p>
 435 <pre>
 436     members() function removed.
 437     Documentation corrected and extended.
 438     Use of struct() in a subclass prohibited.
 439     User definition of accessor allowed.
 440     Treatment of '*' in element types corrected.
 441     Treatment of classes as element types corrected.
 442     Class name to struct() made optional.
 443     Diagnostic checks added.</pre>
 444 <p>Originally <code>Class::Template</code> by Dean Roehrich.</p>
 445 <pre>
 446     # Template.pm   --- struct/member template builder
 447     #   12mar95
 448     #   Dean Roehrich
 449     #
 450     # changes/bugs fixed since 28nov94 version:
 451     #  - podified
 452     # changes/bugs fixed since 21nov94 version:
 453     #  - Fixed examples.
 454     # changes/bugs fixed since 02sep94 version:
 455     #  - Moved to Class::Template.
 456     # changes/bugs fixed since 20feb94 version:
 457     #  - Updated to be a more proper module.
 458     #  - Added &quot;use strict&quot;.
 459     #  - Bug in build_methods, was using @var when @$var needed.
 460     #  - Now using my() rather than local().
 461     #
 462     # Uses perl5 classes to create nested data types.
 463     # This is offered as one implementation of Tom Christiansen's &quot;structs.pl&quot;
 464     # idea.</pre>
 465 <table border="0" width="100%" cellspacing="0" cellpadding="3">
 466 <tr><td class="block" style="background-color: #cccccc" valign="middle">
 467 <big><strong><span class="block">&nbsp;Class::Struct - declare struct-like datatypes as Perl classes</span></strong></big>
 468 </td></tr>
 469 </table>
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