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.\" ========================================================================
.\"
.IX Title "Data::Visitor::Callback 3"
.TH Data::Visitor::Callback 3 "2020-08-02" "perl v5.26.3" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
Data::Visitor::Callback \- A Data::Visitor with callbacks.
.SH "VERSION"
.IX Header "VERSION"
version 0.31
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&        use Data::Visitor::Callback;
\&
\&        my $v = Data::Visitor::Callback\->new(
\&                # you can provide callbacks
\&                # $_ will contain the visited value
\&
\&                value => sub { ... },
\&                array => sub { ... },
\&
\&
\&                # you can also delegate to method names
\&                # this specific example will force traversal on objects, by using the
\&                # \*(Aqvisit_ref\*(Aq callback which normally traverse unblessed references
\&
\&                object => "visit_ref",
\&
\&
\&                # you can also use class names as callbacks
\&                # the callback will be invoked on all objects which inherit that class
\&
\&                \*(AqSome::Class\*(Aq => sub {
\&                        my ( $v, $obj ) = @_; # $v is the visitor
\&
\&                        ...
\&                },
\&        );
\&
\&        $v\->visit( $some_perl_value );
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This is a Data::Visitor subclass that lets you invoke callbacks instead of
needing to subclass yourself.
.SH "METHODS"
.IX Header "METHODS"
.ie n .IP "new %opts, %callbacks" 4
.el .IP "new \f(CW%opts\fR, \f(CW%callbacks\fR" 4
.IX Item "new %opts, %callbacks"
Construct a new visitor.
.Sp
The options supported are:
.RS 4
.IP "ignore_return_values" 4
.IX Item "ignore_return_values"
When this is true (off by default) the return values from the callbacks are
ignored, thus disabling the fmapping behavior as documented in
Data::Visitor.
.Sp
This is useful when you want to modify \f(CW$_\fR directly
.IP "tied_as_objects" 4
.IX Item "tied_as_objects"
Whether or not to visit the \*(L"tied\*(R" in perlfunc of a tied structure instead of
pretending the structure is just a normal one.
.Sp
See \*(L"visit_tied\*(R" in Data::Visitor.
.RE
.RS 4
.RE
.SH "CALLBACKS"
.IX Header "CALLBACKS"
Use these keys for the corresponding callbacks.
.PP
The callback is in the form:
.PP
.Vb 2
\&        sub {
\&                my ( $visitor, $data ) = @_;
\&
\&                # or you can use $_, it\*(Aqs aliased
\&
\&                return $data; # or modified data
\&        }
.Ve
.PP
Within the callback \f(CW$_\fR is aliased to the data, and this is also passed in the
parameter list.
.PP
Any method can also be used as a callback:
.PP
.Vb 1
\&        object => "visit_ref", # visit objects anyway
.Ve
.IP "visit" 4
.IX Item "visit"
Called for all values
.IP "value" 4
.IX Item "value"
Called for non objects, non container (hash, array, glob or scalar ref) values.
.IP "ref_value" 4
.IX Item "ref_value"
Called after \f(CW\*(C`value\*(C'\fR, for references to regexes, globs and code.
.IP "plain_value" 4
.IX Item "plain_value"
Called after \f(CW\*(C`value\*(C'\fR for non references.
.IP "object" 4
.IX Item "object"
Called for blessed objects.
.Sp
Since \*(L"visit_object\*(R" in Data::Visitor will not recurse downwards unless you
delegate to \f(CW\*(C`visit_ref\*(C'\fR, you can specify \f(CW\*(C`visit_ref\*(C'\fR as the callback for
\&\f(CW\*(C`object\*(C'\fR in order to enter objects.
.Sp
It is recommended that you specify the classes (or base classes) you want
though, instead of just visiting any object forcefully.
.IP "Some::Class" 4
.IX Item "Some::Class"
You can use any class name as a callback. This is called only after the
\&\f(CW\*(C`object\*(C'\fR callback.
.Sp
If the object \f(CW\*(C`isa\*(C'\fR the class then the callback will fire.
.Sp
These callbacks are called from least derived to most derived by comparing the
classes' \f(CW\*(C`isa\*(C'\fR at construction time.
.IP "object_no_class" 4
.IX Item "object_no_class"
Called for every object that did not have a class callback.
.IP "object_final" 4
.IX Item "object_final"
The last callback called for objects, useful if you want to post process the
output of any class callbacks.
.IP "array" 4
.IX Item "array"
Called for array references.
.IP "hash" 4
.IX Item "hash"
Called for hash references.
.IP "glob" 4
.IX Item "glob"
Called for glob references.
.IP "scalar" 4
.IX Item "scalar"
Called for scalar references.
.IP "tied" 4
.IX Item "tied"
Called on the return value of \f(CW\*(C`tied\*(C'\fR for all tied containers. Also passes in
the variable as the second argument.
.IP "seen" 4
.IX Item "seen"
Called for a reference value encountered a second time.
.Sp
Passes in the result mapping as the second argument.
.SH "SUPPORT"
.IX Header "SUPPORT"
Bugs may be submitted through the \s-1RT\s0 bug tracker <https://rt.cpan.org/Public/Dist/Display.html?Name=Data-Visitor>
(or bug\-Data\-Visitor@rt.cpan.org <mailto:bug-Data-Visitor@rt.cpan.org>).
.SH "AUTHORS"
.IX Header "AUTHORS"
.IP "\(bu" 4
Yuval Kogman <nothingmuch@woobling.org>
.IP "\(bu" 4
Marcel Grünauer <marcel@cpan.org>
.SH "COPYRIGHT AND LICENCE"
.IX Header "COPYRIGHT AND LICENCE"
This software is copyright (c) 2020 by Yuval Kogman.
.PP
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.