This is a live mirror of the Perl 5 development currently hosted at https://github.com/perl/perl5
Use B<> for options in Class::Struct pod
[perl5.git] / lib / Class / Struct.pm
CommitLineData
8cc95fdb
PP
1package Class::Struct;
2
3## See POD after __END__
4
5require 5.002;
6
7use strict;
8use vars qw(@ISA @EXPORT);
9
10use Carp;
11
12require Exporter;
13@ISA = qw(Exporter);
14@EXPORT = qw(struct);
15
16## Tested on 5.002 and 5.003 without class membership tests:
17my $CHECK_CLASS_MEMBERSHIP = ($] >= 5.003_95);
18
19my $print = 0;
20sub printem {
21 if (@_) { $print = shift }
22 else { $print++ }
23}
24
25{
26 package Class::Struct::Tie_ISA;
27
28 sub TIEARRAY {
29 my $class = shift;
30 return bless [], $class;
31 }
32
33 sub STORE {
34 my ($self, $index, $value) = @_;
35 Class::Struct::_subclass_error();
36 }
37
38 sub FETCH {
39 my ($self, $index) = @_;
40 $self->[$index];
41 }
42
43 sub DESTROY { }
44}
45
46sub struct {
47
48 # Determine parameter list structure, one of:
49 # struct( class => [ element-list ])
50 # struct( class => { element-list })
51 # struct( element-list )
52 # Latter form assumes current package name as struct name.
53
54 my ($class, @decls);
55 my $base_type = ref $_[1];
56 if ( $base_type eq 'HASH' ) {
57 $class = shift;
58 @decls = %{shift()};
59 _usage_error() if @_;
60 }
61 elsif ( $base_type eq 'ARRAY' ) {
62 $class = shift;
63 @decls = @{shift()};
64 _usage_error() if @_;
65 }
66 else {
67 $base_type = 'ARRAY';
68 $class = (caller())[0];
69 @decls = @_;
70 }
71 _usage_error() if @decls % 2 == 1;
72
73 # Ensure we are not, and will not be, a subclass.
74
75 my $isa = do {
76 no strict 'refs';
77 \@{$class . '::ISA'};
78 };
79 _subclass_error() if @$isa;
80 tie @$isa, 'Class::Struct::Tie_ISA';
81
82 # Create constructor.
83
84 croak "function 'new' already defined in package $class"
85 if do { no strict 'refs'; defined &{$class . "::new"} };
86
87 my @methods = ();
88 my %refs = ();
89 my %arrays = ();
90 my %hashes = ();
91 my %classes = ();
92 my $got_class = 0;
93 my $out = '';
94
95 $out = "{\n package $class;\n use Carp;\n sub new {\n";
96
97 my $cnt = 0;
98 my $idx = 0;
99 my( $cmt, $name, $type, $elem );
100
101 if( $base_type eq 'HASH' ){
102 $out .= " my(\$r) = {};\n";
103 $cmt = '';
104 }
105 elsif( $base_type eq 'ARRAY' ){
106 $out .= " my(\$r) = [];\n";
107 }
108 while( $idx < @decls ){
109 $name = $decls[$idx];
110 $type = $decls[$idx+1];
111 push( @methods, $name );
112 if( $base_type eq 'HASH' ){
113 $elem = "{'$name'}";
114 }
115 elsif( $base_type eq 'ARRAY' ){
116 $elem = "[$cnt]";
117 ++$cnt;
118 $cmt = " # $name";
119 }
120 if( $type =~ /^\*(.)/ ){
121 $refs{$name}++;
122 $type = $1;
123 }
124 if( $type eq '@' ){
125 $out .= " \$r->$elem = [];$cmt\n";
126 $arrays{$name}++;
127 }
128 elsif( $type eq '%' ){
129 $out .= " \$r->$elem = {};$cmt\n";
130 $hashes{$name}++;
131 }
132 elsif ( $type eq '$') {
133 $out .= " \$r->$elem = undef;$cmt\n";
134 }
135 elsif( $type =~ /^\w+(?:::\w+)*$/ ){
136 $out .= " \$r->$elem = '${type}'->new();$cmt\n";
137 $classes{$name} = $type;
138 $got_class = 1;
139 }
140 else{
141 croak "'$type' is not a valid struct element type";
142 }
143 $idx += 2;
144 }
145 $out .= " bless \$r;\n }\n";
146
147 # Create accessor methods.
148
149 if ( $got_class && $CHECK_CLASS_MEMBERSHIP ) {
150 $out .= " use UNIVERSAL;\n";
151 }
152 my( $pre, $pst, $sel );
153 $cnt = 0;
154 foreach $name (@methods){
155 if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
156 carp "function '$name' already defined, overrides struct accessor method"
157 if $^W;
158 }
159 else {
160 $pre = $pst = $cmt = $sel = '';
161 if( defined $refs{$name} ){
162 $pre = "\\(";
163 $pst = ")";
164 $cmt = " # returns ref";
165 }
166 $out .= " sub $name {$cmt\n my \$r = shift;\n";
167 if( $base_type eq 'ARRAY' ){
168 $elem = "[$cnt]";
169 ++$cnt;
170 }
171 elsif( $base_type eq 'HASH' ){
172 $elem = "{'$name'}";
173 }
174 if( defined $arrays{$name} ){
175 $out .= " my \$i;\n";
176 $out .= " \@_ ? (\$i = shift) : return $pre\$r->$elem$pst;\n";
177 $sel = "->[\$i]";
178 }
179 elsif( defined $hashes{$name} ){
180 $out .= " my \$i;\n";
181 $out .= " \@_ ? (\$i = shift) : return $pre\$r->$elem$pst;\n";
182 $sel = "->{\$i}";
183 }
184 elsif( defined $classes{$name} ){
185 if ( $CHECK_CLASS_MEMBERSHIP ) {
186 $out .= " croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$type');\n";
187 }
188 }
189 $out .= " croak 'Too many args to $name' if \@_ > 1;\n";
190 $out .= " \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
191 $out .= " }\n";
192 }
193 }
194 $out .= "}\n1;\n";
195
196 print $out if $print;
197 my $result = eval $out;
198 carp $@ if $@;
199}
200
201sub _usage_error {
202 confess "struct usage error";
203}
204
205sub _subclass_error {
206 croak 'struct class cannot be a subclass (@ISA not allowed)';
207}
208
2091; # for require
210
211
212__END__
213
214=head1 NAME
215
216Class::Struct - declare struct-like datatypes as Perl classes
217
218=head1 SYNOPSIS
219
220 use Class::Struct;
221 # declare struct, based on array:
222 struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
223 # declare struct, based on hash:
224 struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
225
226 package CLASS_NAME;
227 use Class::Struct;
228 # declare struct, based on array, implicit class name:
229 struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
230
231
232 package Myobj;
233 use Class::Struct;
234 # declare struct with four types of elements:
235 struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
236
237 $obj = new Myobj; # constructor
238
239 # scalar type accessor:
240 $element_value = $obj->s; # element value
241 $obj->s('new value'); # assign to element
242
243 # array type accessor:
244 $ary_ref = $obj->a; # reference to whole array
245 $ary_element_value = $obj->a(2); # array element value
246 $obj->a(2, 'new value'); # assign to array element
247
248 # hash type accessor:
249 $hash_ref = $obj->h; # reference to whole hash
250 $hash_element_value = $obj->h('x'); # hash element value
251 $obj->h('x', 'new value'); # assign to hash element
252
253 # class type accessor:
254 $element_value = $obj->c; # object reference
255 $obj->c->method(...); # call method of object
256 $obj->c(new My_Other_Class); # assign a new object
257
258
259=head1 DESCRIPTION
260
261C<Class::Struct> exports a single function, C<struct>.
262Given a list of element names and types, and optionally
263a class name, C<struct> creates a Perl 5 class that implements
264a "struct-like" data structure.
265
266The new class is given a constructor method, C<new>, for creating
267struct objects.
268
269Each element in the struct data has an accessor method, which is
270used to assign to the element and to fetch its value. The
271default accessor can be overridden by declaring a C<sub> of the
272same name in the package. (See Example 2.)
273
274Each element's type can be scalar, array, hash, or class.
275
276
277=head2 The C<struct()> function
278
279The C<struct> function has three forms of parameter-list.
280
281 struct( CLASS_NAME => [ ELEMENT_LIST ]);
282 struct( CLASS_NAME => { ELEMENT_LIST });
283 struct( ELEMENT_LIST );
284
285The first and second forms explicitly identify the name of the
286class being created. The third form assumes the current package
287name as the class name.
288
289An object of a class created by the first and third forms is
290based on an array, whereas an object of a class created by the
291second form is based on a hash. The array-based forms will be
292somewhat faster and smaller; the hash-based forms are more
293flexible.
294
295The class created by C<struct> must not be a subclass of another
296class other than C<UNIVERSAL>.
297
298A function named C<new> must not be explicitly defined in a class
299created by C<struct>.
300
301The I<ELEMENT_LIST> has the form
302
303 NAME => TYPE, ...
304
305Each name-type pair declares one element of the struct. Each
306element name will be defined as an accessor method unless a
307method by that name is explicitly defined; in the latter case, a
103ff8e3 308warning is issued if the warning flag (B<-w>) is set.
8cc95fdb
PP
309
310
311=head2 Element Types and Accessor Methods
312
313The four element types -- scalar, array, hash, and class -- are
314represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
315optionally preceded by a C<'*'>.
316
317The accessor method provided by C<struct> for an element depends
318on the declared type of the element.
319
320=over
321
322=item Scalar (C<'$'> or C<'*$'>)
323
324The element is a scalar, and is initialized to C<undef>.
325
326The accessor's argument, if any, is assigned to the element.
327
328If the element type is C<'$'>, the value of the element (after
329assignment) is returned. If the element type is C<'*$'>, a reference
330to the element is returned.
331
332=item Array (C<'@'> or C<'*@'>)
333
334The element is an array, initialized to C<()>.
335
336With no argument, the accessor returns a reference to the
337element's whole array.
338
339With one or two arguments, the first argument is an index
340specifying one element of the array; the second argument, if
341present, is assigned to the array element. If the element type
342is C<'@'>, the accessor returns the array element value. If the
343element type is C<'*@'>, a reference to the array element is
344returned.
345
346=item Hash (C<'%'> or C<'*%'>)
347
348The element is a hash, initialized to C<()>.
349
350With no argument, the accessor returns a reference to the
351element's whole hash.
352
353With one or two arguments, the first argument is a key specifying
354one element of the hash; the second argument, if present, is
355assigned to the hash element. If the element type is C<'%'>, the
356accessor returns the hash element value. If the element type is
357C<'*%'>, a reference to the hash element is returned.
358
359=item Class (C<'Class_Name'> or C<'*Class_Name'>)
360
361The element's value must be a reference blessed to the named
362class or to one of its subclasses. The element is initialized to
363the result of calling the C<new> constructor of the named class.
364
365The accessor's argument, if any, is assigned to the element. The
366accessor will C<croak> if this is not an appropriate object
367reference.
368
369If the element type does not start with a C<'*'>, the accessor
370returns the element value (after assignment). If the element type
371starts with a C<'*'>, a reference to the element itself is returned.
372
373=back
374
375=head1 EXAMPLES
376
377=over
378
379=item Example 1
380
381Giving a struct element a class type that is also a struct is how
382structs are nested. Here, C<timeval> represents a time (seconds and
383microseconds), and C<rusage> has two elements, each of which is of
384type C<timeval>.
385
386 use Class::Struct;
387
388 struct( rusage => {
389 ru_utime => timeval, # seconds
390 ru_stime => timeval, # microseconds
391 });
392
393 struct( timeval => [
394 tv_secs => '$',
395 tv_usecs => '$',
396 ]);
397
398 # create an object:
399 my $t = new rusage;
400 # $t->ru_utime and $t->ru_stime are objects of type timeval.
401
402 # set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
403 $t->ru_utime->tv_secs(100);
404 $t->ru_utime->tv_usecs(0);
405 $t->ru_stime->tv_secs(5);
406 $t->ru_stime->tv_usecs(0);
407
408
409=item Example 2
410
411An accessor function can be redefined in order to provide
412additional checking of values, etc. Here, we want the C<count>
413element always to be nonnegative, so we redefine the C<count>
414accessor accordingly.
415
416 package MyObj;
417 use Class::Struct;
418
419 # declare the struct
420 struct ( 'MyObj', { count => '$', stuff => '%' } );
421
422 # override the default accessor method for 'count'
423 sub count {
424 my $self = shift;
425 if ( @_ ) {
426 die 'count must be nonnegative' if $_[0] < 0;
427 $self->{'count'} = shift;
428 warn "Too many args to count" if @_;
429 }
430 return $self->{'count'};
431 }
432
433 package main;
434 $x = new MyObj;
435 print "\$x->count(5) = ", $x->count(5), "\n";
436 # prints '$x->count(5) = 5'
437
438 print "\$x->count = ", $x->count, "\n";
439 # prints '$x->count = 5'
440
441 print "\$x->count(-5) = ", $x->count(-5), "\n";
442 # dies due to negative argument!
443
444
445=head1 Author and Modification History
446
447
448Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
449
450 members() function removed.
451 Documentation corrected and extended.
452 Use of struct() in a subclass prohibited.
453 User definition of accessor allowed.
454 Treatment of '*' in element types corrected.
455 Treatment of classes as element types corrected.
456 Class name to struct() made optional.
457 Diagnostic checks added.
458
459
460Originally C<Class::Template> by Dean Roehrich.
461
462 # Template.pm --- struct/member template builder
463 # 12mar95
464 # Dean Roehrich
465 #
466 # changes/bugs fixed since 28nov94 version:
467 # - podified
468 # changes/bugs fixed since 21nov94 version:
469 # - Fixed examples.
470 # changes/bugs fixed since 02sep94 version:
471 # - Moved to Class::Template.
472 # changes/bugs fixed since 20feb94 version:
473 # - Updated to be a more proper module.
474 # - Added "use strict".
475 # - Bug in build_methods, was using @var when @$var needed.
476 # - Now using my() rather than local().
477 #
478 # Uses perl5 classes to create nested data types.
479 # This is offered as one implementation of Tom Christiansen's "structs.pl"
480 # idea.
481
482=cut