xref: /openbsd-src/gnu/usr.bin/perl/lib/Class/Struct.pm (revision ba47ec9da08b5e716a167fd61325b8edfcb66dd6)
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    my( $pre, $pst, $sel );
150    $cnt = 0;
151    foreach $name (@methods){
152        if ( do { no strict 'refs'; defined &{$class . "::$name"} } ) {
153            carp "function '$name' already defined, overrides struct accessor method"
154                if $^W;
155        }
156        else {
157            $pre = $pst = $cmt = $sel = '';
158            if( defined $refs{$name} ){
159                $pre = "\\(";
160                $pst = ")";
161                $cmt = " # returns ref";
162            }
163            $out .= "  sub $name {$cmt\n    my \$r = shift;\n";
164            if( $base_type eq 'ARRAY' ){
165                $elem = "[$cnt]";
166                ++$cnt;
167            }
168            elsif( $base_type eq 'HASH' ){
169                $elem = "{'$name'}";
170            }
171            if( defined $arrays{$name} ){
172                $out .= "    my \$i;\n";
173                $out .= "    \@_ ? (\$i = shift) : return $pre\$r->$elem$pst;\n";
174                $sel = "->[\$i]";
175            }
176            elsif( defined $hashes{$name} ){
177                $out .= "    my \$i;\n";
178                $out .= "    \@_ ? (\$i = shift) : return $pre\$r->$elem$pst;\n";
179                $sel = "->{\$i}";
180            }
181            elsif( defined $classes{$name} ){
182                if ( $CHECK_CLASS_MEMBERSHIP ) {
183                    $out .= "    croak '$name argument is wrong class' if \@_ && ! UNIVERSAL::isa(\$_[0], '$type');\n";
184                }
185            }
186            $out .= "    croak 'Too many args to $name' if \@_ > 1;\n";
187            $out .= "    \@_ ? ($pre\$r->$elem$sel = shift$pst) : $pre\$r->$elem$sel$pst;\n";
188            $out .= "  }\n";
189        }
190    }
191    $out .= "}\n1;\n";
192
193    print $out if $print;
194    my $result = eval $out;
195    carp $@ if $@;
196}
197
198sub _usage_error {
199    confess "struct usage error";
200}
201
202sub _subclass_error {
203    croak 'struct class cannot be a subclass (@ISA not allowed)';
204}
205
2061; # for require
207
208
209__END__
210
211=head1 NAME
212
213Class::Struct - declare struct-like datatypes as Perl classes
214
215=head1 SYNOPSIS
216
217    use Class::Struct;
218            # declare struct, based on array:
219    struct( CLASS_NAME => [ ELEMENT_NAME => ELEMENT_TYPE, ... ]);
220            # declare struct, based on hash:
221    struct( CLASS_NAME => { ELEMENT_NAME => ELEMENT_TYPE, ... });
222
223    package CLASS_NAME;
224    use Class::Struct;
225            # declare struct, based on array, implicit class name:
226    struct( ELEMENT_NAME => ELEMENT_TYPE, ... );
227
228
229    package Myobj;
230    use Class::Struct;
231            # declare struct with four types of elements:
232    struct( s => '$', a => '@', h => '%', c => 'My_Other_Class' );
233
234    $obj = new Myobj;               # constructor
235
236                                    # scalar type accessor:
237    $element_value = $obj->s;           # element value
238    $obj->s('new value');               # assign to element
239
240                                    # array type accessor:
241    $ary_ref = $obj->a;                 # reference to whole array
242    $ary_element_value = $obj->a(2);    # array element value
243    $obj->a(2, 'new value');            # assign to array element
244
245                                    # hash type accessor:
246    $hash_ref = $obj->h;                # reference to whole hash
247    $hash_element_value = $obj->h('x'); # hash element value
248    $obj->h('x', 'new value');        # assign to hash element
249
250                                    # class type accessor:
251    $element_value = $obj->c;           # object reference
252    $obj->c->method(...);               # call method of object
253    $obj->c(new My_Other_Class);        # assign a new object
254
255
256=head1 DESCRIPTION
257
258C<Class::Struct> exports a single function, C<struct>.
259Given a list of element names and types, and optionally
260a class name, C<struct> creates a Perl 5 class that implements
261a "struct-like" data structure.
262
263The new class is given a constructor method, C<new>, for creating
264struct objects.
265
266Each element in the struct data has an accessor method, which is
267used to assign to the element and to fetch its value.  The
268default accessor can be overridden by declaring a C<sub> of the
269same name in the package.  (See Example 2.)
270
271Each element's type can be scalar, array, hash, or class.
272
273
274=head2 The C<struct()> function
275
276The C<struct> function has three forms of parameter-list.
277
278    struct( CLASS_NAME => [ ELEMENT_LIST ]);
279    struct( CLASS_NAME => { ELEMENT_LIST });
280    struct( ELEMENT_LIST );
281
282The first and second forms explicitly identify the name of the
283class being created.  The third form assumes the current package
284name as the class name.
285
286An object of a class created by the first and third forms is
287based on an array, whereas an object of a class created by the
288second form is based on a hash. The array-based forms will be
289somewhat faster and smaller; the hash-based forms are more
290flexible.
291
292The class created by C<struct> must not be a subclass of another
293class other than C<UNIVERSAL>.
294
295A function named C<new> must not be explicitly defined in a class
296created by C<struct>.
297
298The I<ELEMENT_LIST> has the form
299
300    NAME => TYPE, ...
301
302Each name-type pair declares one element of the struct. Each
303element name will be defined as an accessor method unless a
304method by that name is explicitly defined; in the latter case, a
305warning is issued if the warning flag (B<-w>) is set.
306
307
308=head2 Element Types and Accessor Methods
309
310The four element types -- scalar, array, hash, and class -- are
311represented by strings -- C<'$'>, C<'@'>, C<'%'>, and a class name --
312optionally preceded by a C<'*'>.
313
314The accessor method provided by C<struct> for an element depends
315on the declared type of the element.
316
317=over
318
319=item Scalar (C<'$'> or C<'*$'>)
320
321The element is a scalar, and is initialized to C<undef>.
322
323The accessor's argument, if any, is assigned to the element.
324
325If the element type is C<'$'>, the value of the element (after
326assignment) is returned. If the element type is C<'*$'>, a reference
327to the element is returned.
328
329=item Array (C<'@'> or C<'*@'>)
330
331The element is an array, initialized to C<()>.
332
333With no argument, the accessor returns a reference to the
334element's whole array.
335
336With one or two arguments, the first argument is an index
337specifying one element of the array; the second argument, if
338present, is assigned to the array element.  If the element type
339is C<'@'>, the accessor returns the array element value.  If the
340element type is C<'*@'>, a reference to the array element is
341returned.
342
343=item Hash (C<'%'> or C<'*%'>)
344
345The element is a hash, initialized to C<()>.
346
347With no argument, the accessor returns a reference to the
348element's whole hash.
349
350With one or two arguments, the first argument is a key specifying
351one element of the hash; the second argument, if present, is
352assigned to the hash element.  If the element type is C<'%'>, the
353accessor returns the hash element value.  If the element type is
354C<'*%'>, a reference to the hash element is returned.
355
356=item Class (C<'Class_Name'> or C<'*Class_Name'>)
357
358The element's value must be a reference blessed to the named
359class or to one of its subclasses. The element is initialized to
360the result of calling the C<new> constructor of the named class.
361
362The accessor's argument, if any, is assigned to the element. The
363accessor will C<croak> if this is not an appropriate object
364reference.
365
366If the element type does not start with a C<'*'>, the accessor
367returns the element value (after assignment). If the element type
368starts with a C<'*'>, a reference to the element itself is returned.
369
370=back
371
372=head1 EXAMPLES
373
374=over
375
376=item Example 1
377
378Giving a struct element a class type that is also a struct is how
379structs are nested.  Here, C<timeval> represents a time (seconds and
380microseconds), and C<rusage> has two elements, each of which is of
381type C<timeval>.
382
383    use Class::Struct;
384
385    struct( rusage => {
386        ru_utime => timeval,  # seconds
387        ru_stime => timeval,  # microseconds
388    });
389
390    struct( timeval => [
391        tv_secs  => '$',
392        tv_usecs => '$',
393    ]);
394
395        # create an object:
396    my $t = new rusage;
397    	# $t->ru_utime and $t->ru_stime are objects of type timeval.
398
399        # set $t->ru_utime to 100.0 sec and $t->ru_stime to 5.0 sec.
400    $t->ru_utime->tv_secs(100);
401    $t->ru_utime->tv_usecs(0);
402    $t->ru_stime->tv_secs(5);
403    $t->ru_stime->tv_usecs(0);
404
405
406=item Example 2
407
408An accessor function can be redefined in order to provide
409additional checking of values, etc.  Here, we want the C<count>
410element always to be nonnegative, so we redefine the C<count>
411accessor accordingly.
412
413    package MyObj;
414    use Class::Struct;
415
416    		# declare the struct
417    struct ( 'MyObj', { count => '$', stuff => '%' } );
418
419    		# override the default accessor method for 'count'
420    sub count {
421        my $self = shift;
422        if ( @_ ) {
423            die 'count must be nonnegative' if $_[0] < 0;
424            $self->{'count'} = shift;
425            warn "Too many args to count" if @_;
426        }
427        return $self->{'count'};
428    }
429
430    package main;
431    $x = new MyObj;
432    print "\$x->count(5) = ", $x->count(5), "\n";
433                            # prints '$x->count(5) = 5'
434
435    print "\$x->count = ", $x->count, "\n";
436                            # prints '$x->count = 5'
437
438    print "\$x->count(-5) = ", $x->count(-5), "\n";
439                            # dies due to negative argument!
440
441
442=head1 Author and Modification History
443
444
445Renamed to C<Class::Struct> and modified by Jim Miner, 1997-04-02.
446
447    members() function removed.
448    Documentation corrected and extended.
449    Use of struct() in a subclass prohibited.
450    User definition of accessor allowed.
451    Treatment of '*' in element types corrected.
452    Treatment of classes as element types corrected.
453    Class name to struct() made optional.
454    Diagnostic checks added.
455
456
457Originally C<Class::Template> by Dean Roehrich.
458
459    # Template.pm   --- struct/member template builder
460    #   12mar95
461    #   Dean Roehrich
462    #
463    # changes/bugs fixed since 28nov94 version:
464    #  - podified
465    # changes/bugs fixed since 21nov94 version:
466    #  - Fixed examples.
467    # changes/bugs fixed since 02sep94 version:
468    #  - Moved to Class::Template.
469    # changes/bugs fixed since 20feb94 version:
470    #  - Updated to be a more proper module.
471    #  - Added "use strict".
472    #  - Bug in build_methods, was using @var when @$var needed.
473    #  - Now using my() rather than local().
474    #
475    # Uses perl5 classes to create nested data types.
476    # This is offered as one implementation of Tom Christiansen's "structs.pl"
477    # idea.
478
479=cut
480