1Flow(3) User Contributed Perl Documentation Flow(3)
2
6 Data::Flow - Perl extension for simple-minded recipe-controlled build
7 of data.
8
10 use Data::Flow;
11 $recipes = { path => { default => './MANIFEST'},
12 contents => { prerequisites => ['path', 'x'] ,
13 process =>
14 sub {
15 my $data = shift;
16 $data->{ shift() } = `cat $data->{'path'}`
17 x $data->{'x'};
18 }
19 },
20 };
21 $request = new Data::Flow $recipes;
23 $request->set( x => 1);
24 print $request->get('contents');
25 tie %request, Data::Flow, $recipes;
27 $request{x} = 1;
28 print $request{contents};
29
31 The module Data::Flow provides its services via objects. The objects
32 may be obtained by the usual
33 $request = new Data::Flow $recipes;
35 paradigm. The argument $recipes is a hash reference, which provides the
37 rules for request processing. The objects support three methods, set(),
38 get(), aget(), and already_set(). The first one is used to provide
39 input data for processing, the second one to obtain the output. The
40 third one to obtain a reference to an array with results of repeated
41 get(), and the last one to query whether a field is already known.
42 The unit of requested information is a field. The method set() takes a
44 pair "field => value", the methods get() and already_set() take one
45 argument: the "field", and the method aget() takes multiple fields.
46 Every object is created without any fields filled, but it knows how to
48 construct fields basing on other fields or some global into. This
49 knowledge is provided in the argument $recipe of the new() function.
50 This is a reference to a hash, keyed by fields. The values of this hash
51 are hash references themselves, which describe how to acquire the field
52 which is the corresponding key of the initial hash.
53 The internal hashes may have the following keys:
55 "default"
57 describes the default value for the key, if none is provided by
58 set(). The value becomes the value of the field of the object.
59 No additional processing is performed. Example:
60 default => $Config{installdir}
62 "prerequisites"
64 gives the fields which are needed for the construction of the
65 given field. The corresponding value is an array references.
66 The array contains the required fields.
67 If "defaults" did not satisfy the request for a field, but
69 "$recipe->{field}{prerequisites}" exists, the required fields
70 are build before any further processing is done. Example:
71 prerequisites => [ qw(prefix arch) ]
73 "process"
75 contains the rule to build the field. The value is a reference
76 to a subroutine taking 2 arguments: the reference to a hash
77 with all the fields which have been set, and the name of the
78 required field. It is up to the subroutine to actually fill the
79 corresponding field of the hash, an error condition is raised
80 if it did not. Example:
81 process => sub { my $data = shift;
83 $data->{time} = localtime(time) } }
84 "oo_process"
86 contains the rule to build the field. The value is a reference
87 to a subroutine taking 2 arguments: the object $request, and
88 the name of the required field. It is up to the subroutine to
89 actually fill the corresponding field of $request, an error
90 condition is raised if it did not. Example:
91 oo_process => sub { my $data = shift;
93 $data->set( time => localtime(time) ) }
94 "output"
96 the corresponing value has the same meaning as for "process",
97 but the return value of the subroutine is used as the value of
98 the field. Example:
99 output => sub { localtime(time) }
101 "oo_output"
103 the corresponing value has the same meaning as for "process",
104 but the return value of the method is used as the value of the
105 field. Example:
106 output => sub { my $self = shift; $self->get('r') . localtime(time) }
108 "filter"
110 contains the rule to build the field basing on other fields.
111 The value is a reference to an array. The first element of the
112 array is a reference to a subroutine, the rest contains names
113 of the fields. When the subroutine is called, the arguments are
114 the values of fields of the object $request which appear in the
115 array (in the same order). The return value of the subroutine
116 is used as the value of the field. Example:
117 filter => [ sub { shift + shift },
119 'first_half', 'second_half' ]
120 Note that the mentioned field will be automatically marked as
122 prerequisites.
123 "self_filter"
125 is similar to "filter", but an extra argument, the object
126 itself, is put in front of the list of arguments. Example:
127 self_filter => [ sub { my ($self, $first_half = (shift, shift);
129 $first_half *= -$self->get('total')*100
130 if $first_half < 0; # negative means percentage
131 $first_half + shift },
132 'first_half', 'second_half' ]
133 "class_filter"
135 is similar to "filter", but the first argument is the name of
136 the method to call, second one is the name of the package to
137 use for the method invocation. The rest contains names of field
138 to provide as method arguments. Example:
139 class_filter => [ 'new', 'FileHandle', 'filename' ]
141 "method_filter"
143 is similar to "class_filter", but the second argument is the
144 name of the field which is used to call the method upon.
145 Example:
146 method_filter => [ 'show', 'widget_name', 'current_display' ]
148 Tied interface
150 The access to the same functionality is available via tied hash
151 interface.
152
154 Ilya Zakharevich, cpan@ilyaz.org, with multiple additions from Terrence
155 Monroe Brannon and Radoslav Nedyalkov.
156
158 perl(1), make(1).
159perl v5.34.0 2021-07-22 Flow(3)