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Template::Context(3)	       User Contributed Perl Documentation	     Template::Context(3)

NAME
       Template::Context - Runtime context in which templates are processed

SYNOPSIS
	   use Template::Context;

	   # constructor
	   $context = Template::Context->new(\%config)
	       || die $Template::Context::ERROR;

	   # fetch (load and compile) a template
	   $template = $context->template($template_name);

	   # fetch (load and instantiate) a plugin object
	   $plugin = $context->plugin($name, \@args);

	   # fetch (return or create) a filter subroutine
	   $filter = $context->filter($name, \@args, $alias);

	   # process/include a template, errors are thrown via die()
	   $output = $context->process($template, \%vars);
	   $output = $context->include($template, \%vars);

	   # raise an exception via die()
	   $context->throw($error_type, $error_message, \$output_buffer);

	   # catch an exception, clean it up and fix output buffer
	   $exception = $context->catch($exception, \$output_buffer);

	   # save/restore the stash to effect variable localisation
	   $new_stash = $context->localise(\%vars);
	   $old_stash = $context->delocalise();

	   # add new BLOCK or FILTER definitions
	   $context->define_block($name, $block);
	   $context->define_filter($name, \&filtersub, $is_dynamic);

	   # reset context, clearing any imported BLOCK definitions
	   $context->reset();

	   # methods for accessing internal items
	   $stash     = $context->stash();
	   $tflag     = $context->trim();
	   $epflag    = $context->eval_perl();
	   $providers = $context->templates();
	   $providers = $context->plugins();
	   $providers = $context->filters();
	   ...

DESCRIPTION
       The "Template::Context" module defines an object class for representing a runtime context
       in which templates are processed.  It provides an interface to the fundamental operations
       of the Template Toolkit processing engine through which compiled templates (i.e. Perl code
       constructed from the template source) can process templates, load plugins and filters,
       raise exceptions and so on.

       A default "Template::Context" object is created by the Template module.	Any
       "Template::Context" options may be passed to the Template new() constructor method and
       will be forwarded to the "Template::Context" constructor.

	   use Template;

	   my $template = Template->new({
	       TRIM	 => 1,
	       EVAL_PERL => 1,
	       BLOCKS	 => {
		   header => 'This is the header',
		   footer => 'This is the footer',
	       },
	   });

       Similarly, the "Template::Context" constructor will forward all configuration parameters
       onto other default objects (e.g. Template::Provider, Template::Plugins, Template::Filters,
       etc.) that it may need to instantiate.

	   $context = Template::Context->new({
	       INCLUDE_PATH => '/home/abw/templates', # provider option
	       TAG_STYLE    => 'html',		      # parser option
	   });

       A "Template::Context" object (or subclass) can be explicitly instantiated and passed to
       the Template new() constructor method as the "CONTEXT" configuration item.

	   use Template;
	   use Template::Context;

	   my $context	= Template::Context->new({ TRIM => 1 });
	   my $template = Template->new({ CONTEXT => $context });

       The Template module uses the Template::Config context() factory method to create a default
       context object when required. The $Template::Config::CONTEXT package variable may be set
       to specify an alternate context module. This will be loaded automatically and its new()
       constructor method called by the context() factory method when a default context object is
       required.

	   use Template;

	   $Template::Config::CONTEXT = 'MyOrg::Template::Context';

	   my $template = Template->new({
	       EVAL_PERL   => 1,
	       EXTRA_MAGIC => 'red hot',  # your extra config items
	       ...
	   });

METHODS
   new(\%params)
       The "new()" constructor method is called to instantiate a "Template::Context" object.
       Configuration parameters may be specified as a HASH reference or as a list of "name =>
       value" pairs.

	   my $context = Template::Context->new({
	       INCLUDE_PATH => 'header',
	       POST_PROCESS => 'footer',
	   });

	   my $context = Template::Context->new( EVAL_PERL => 1 );

       The "new()" method returns a "Template::Context" object or "undef" on error. In the latter
       case, a relevant error message can be retrieved by the error() class method or directly
       from the $Template::Context::ERROR package variable.

	   my $context = Template::Context->new(\%config)
	       || die Template::Context->error();

	   my $context = Template::Context->new(\%config)
	       || die $Template::Context::ERROR;

       The following configuration items may be specified.  Please see Template::Manual::Config
       for further details.

       VARIABLES

       The VARIABLES option can be used to specify a hash array of template variables.

	   my $context = Template::Context->new({
	       VARIABLES => {
		   title   => 'A Demo Page',
		   author  => 'Joe Random Hacker',
		   version => 3.14,
	       },
	   };

       BLOCKS

       The BLOCKS option can be used to pre-define a default set of template blocks.

	   my $context = Template::Context->new({
	       BLOCKS => {
		   header  => 'The Header.  [% title %]',
		   footer  => sub { return $some_output_text },
		   another => Template::Document->new({ ... }),
	       },
	   });

       VIEWS

       The VIEWS option can be used to pre-define one or more Template::View objects.

	   my $context = Template::Context->new({
	       VIEWS => [
		   bottom => { prefix => 'bottom/' },
		   middle => { prefix => 'middle/', base => 'bottom' },
		   top	  => { prefix => 'top/',    base => 'middle' },
	       ],
	   });

       TRIM

       The TRIM option can be set to have any leading and trailing whitespace automatically
       removed from the output of all template files and "BLOCK"s.

       example:

	   [% BLOCK foo %]

	   Line 1 of foo

	   [% END %]

	   before
	   [% INCLUDE foo %]
	   after

       output:

	   before
	   Line 1 of foo
	   after

       EVAL_PERL

       The EVAL_PERL is used to indicate if "PERL" and/or "RAWPERL" blocks should be evaluated.
       It is disabled by default.

       RECURSION

       The RECURSION can be set to allow templates to recursively process themselves, either
       directly (e.g. template "foo" calls "INCLUDE foo") or indirectly (e.g.  "foo" calls
       "INCLUDE bar" which calls "INCLUDE foo").

       LOAD_TEMPLATES

       The LOAD_TEMPLATES option can be used to provide a reference to a list of
       Template::Provider objects or sub-classes thereof which will take responsibility for
       loading and compiling templates.

	   my $context = Template::Context->new({
	       LOAD_TEMPLATES => [
		   MyOrg::Template::Provider->new({ ... }),
		   Template::Provider->new({ ... }),
	       ],
	   });

       LOAD_PLUGINS

       The LOAD_PLUGINS options can be used to specify a list of provider objects responsible for
       loading and instantiating template plugin objects.

	   my $context = Template::Context->new({
	       LOAD_PLUGINS => [
		   MyOrg::Template::Plugins->new({ ... }),
		   Template::Plugins->new({ ... }),
	       ],
	   });

       LOAD_FILTERS

       The LOAD_FILTERS option can be used to specify a list of provider objects for returning
       and/or creating filter subroutines.

	   my $context = Template::Context->new({
	       LOAD_FILTERS => [
		   MyTemplate::Filters->new(),
		   Template::Filters->new(),
	       ],
	   });

       STASH

       The STASH option can be used to specify a Template::Stash object or sub-class which will
       take responsibility for managing template variables.

	   my $stash = MyOrg::Template::Stash->new({ ... });
	   my $context = Template::Context->new({
	       STASH => $stash,
	   });

       DEBUG

       The DEBUG option can be used to enable various debugging features of the Template::Context
       module.

	   use Template::Constants qw( :debug );

	   my $template = Template->new({
	       DEBUG => DEBUG_CONTEXT | DEBUG_DIRS,
	   });

   template($name)
       Returns a compiled template by querying each of the LOAD_TEMPLATES providers (instances of
       Template::Provider, or sub-class) in turn.

	   $template = $context->template('header');

       On error, a Template::Exception object of type '"file"' is thrown via "die()".  This can
       be caught by enclosing the call to "template()" in an "eval" block and examining $@.

	   eval { $template = $context->template('header') };
	   if ($@) {
	       print "failed to fetch template: $@\n";
	   }

   plugin($name, \@args)
       Instantiates a plugin object by querying each of the LOAD_PLUGINS providers. The default
       LOAD_PLUGINS provider is a Template::Plugins object which attempts to load plugin modules,
       according the various configuration items such as PLUGIN_BASE, LOAD_PERL, etc., and then
       instantiate an object via new(). A reference to a list of constructor arguments may be
       passed as the second parameter. These are forwarded to the plugin constructor.

       Returns a reference to a plugin (which is generally an object, but doesn't have to be).
       Errors are thrown as Template::Exception objects with the type set to '"plugin"'.

	   $plugin = $context->plugin('DBI', 'dbi:msql:mydbname');

   filter($name, \@args, $alias)
       Instantiates a filter subroutine by querying the LOAD_FILTERS providers.  The default
       LOAD_FILTERS provider is a Template::Filters object.

       Additional arguments may be passed by list reference along with an optional alias under
       which the filter will be cached for subsequent use. The filter is cached under its own
       $name if $alias is undefined. Subsequent calls to "filter($name)" will return the cached
       entry, if defined. Specifying arguments bypasses the caching mechanism and always creates
       a new filter. Errors are thrown as Template::Exception objects with the type set to
       '"filter"'.

	   # static filter (no args)
	   $filter = $context->filter('html');

	   # dynamic filter (args) aliased to 'padright'
	   $filter = $context->filter('format', '%60s', 'padright');

	   # retrieve previous filter via 'padright' alias
	   $filter = $context->filter('padright');

   process($template, \%vars)
       Processes a template named or referenced by the first parameter and returns the output
       generated.  An optional reference to a hash array may be passed as the second parameter,
       containing variable definitions which will be set before the template is processed.  The
       template is processed in the current context, with no localisation of variables performed.
       Errors are thrown as Template::Exception objects via "die()".

	   $output = $context->process('header', { title => 'Hello World' });

   include($template, \%vars)
       Similar to process(), but using localised variables.  Changes made to any variables will
       only persist until the "include()" method completes.

	   $output = $context->include('header', { title => 'Hello World' });

   insert($template)
       This method returns the source content of a template file without performing any
       evaluation.  It is used to implement the "INSERT" directive.

   throw($error_type, $error_message, \$output)
       Raises an exception in the form of a Template::Exception object by calling "die()". This
       method may be passed a reference to an existing Template::Exception object; a single value
       containing an error message which is used to instantiate a Template::Exception of type
       '"undef"'; or a pair of values representing the exception "type" and "info" from which a
       Template::Exception object is instantiated. e.g.

	   $context->throw($exception);
	   $context->throw("I'm sorry Dave, I can't do that");
	   $context->throw('denied', "I'm sorry Dave, I can't do that");

       The optional third parameter may be a reference to the current output buffer.  This is
       then stored in the exception object when created, allowing the catcher to examine and use
       the output up to the point at which the exception was raised.

	   $output .= 'blah blah blah';
	   $output .= 'more rhubarb';
	   $context->throw('yack', 'Too much yacking', \$output);

   catch($exception, \$output)
       Catches an exception thrown, either as a reference to a Template::Exception object or some
       other value. In the latter case, the error string is promoted to a Template::Exception
       object of '"undef"' type. This method also accepts a reference to the current output
       buffer which is passed to the Template::Exception constructor, or is appended to the
       output buffer stored in an existing Template::Exception object, if unique (i.e. not the
       same reference). By this process, the correct state of the output buffer can be
       reconstructed for simple or nested throws.

   define_block($name, $block)
       Adds a new block definition to the internal BLOCKS cache.  The first argument should
       contain the name of the block and the second a reference to a Template::Document object or
       template sub-routine, or template text which is automatically compiled into a template
       sub-routine.

       Returns a true value (the sub-routine or Template::Document reference) on success or undef
       on failure. The relevant error message can be retrieved by calling the error() method.

   define_filter($name, \&filter, $is_dynamic)
       Adds a new filter definition by calling the store() method on each of the LOAD_FILTERS
       providers until accepted (in the usual case, this is accepted straight away by the one and
       only Template::Filters provider). The first argument should contain the name of the filter
       and the second a reference to a filter subroutine. The optional third argument can be set
       to any true value to indicate that the subroutine is a dynamic filter factory.

       Returns a true value or throws a '"filter"' exception on error.

   define_vmethod($type, $name, $code)
       This method is a wrapper around the Template::Stash define_vmethod() method.  It can be
       used to define new virtual methods.

	   # define a new scalar (item) virtual method
	   $context->define_vmethod(
	       item => ucfirst => sub {
		   my $text = shift;
		   return ucfirst $text;
	       }
	   )

   define_view($name, \%params)
       This method allows you to define a named view.

	   $context->define_view(
	       my_view => {
		   prefix => 'my_templates/'
	       }
	   );

       The view is then accessible as a template variable.

	   [% my_view.print(some_data) %]

   define_views($views)
       This method allows you to define multiple named views.  A reference to a hash array or
       list reference should be passed as an argument.

	   $context->define_view({     # hash reference
	       my_view_one => {
		   prefix => 'my_templates_one/'
	       },
	       my_view_two => {
		   prefix => 'my_templates_two/'
	       }
	   });

       If you're defining multiple views of which one or more are based on other views in the
       same definition then you should pass them as a list reference.  This ensures that they get
       created in the right order (Perl does not preserve the order of items defined in a hash
       reference so you can't guarantee that your base class view will be defined before your
       subclass view).

	   $context->define_view([     # list referenence
	       my_view_one => {
		   prefix => 'my_templates_one/'
	       },
	       my_view_two => {
		   prefix => 'my_templates_two/' ,
		   base   => 'my_view_one',
	       }
	   ]);

       The views are then accessible as template variables.

	   [% my_view_one.print(some_data) %]
	   [% my_view_two.print(some_data) %]

       See also the VIEWS option.

   stash()
       This method returns the Template::Stash object used internally to manage template
       variables.

   localise(\%vars)
       Clones the stash to create a context with localised variables.  Returns a reference to the
       newly cloned stash object which is also stored internally.

	   $stash = $context->localise();

   delocalise()
       Restore the stash to its state prior to localisation.

	   $stash = $context->delocalise();

   visit(\%blocks)
       This method is called by Template::Document objects immediately before they process their
       content.  It is called to register any local "BLOCK" definitions with the context object
       so that they may be subsequently delivered on request.

   leave()
       Compliment to the visit() method. Called by Template::Document objects immediately after
       they process their content.

   view()
       This method creates a Template::View object bound to the context.

   reset()
       Clears the local BLOCKS cache of any "BLOCK" definitions.  Any initial set of BLOCKS
       specified as a configuration item to the constructor will be reinstated.

   debugging($flag, @args)
       This method is used to control debugging output.  It is used to implement the DEBUG
       directive.

       The first argument can be "on" or "off" to enable or disable debugging respectively.  The
       numerical values 0 and 1 can also be used if you prefer.

	   $context->debugging('on');

       Alternately, the first argument can be "format" to define a new debug message format.  The
       second argument should be the format string which can contain any of the $file, $line or
       $text symbols to indicate where the relevant values should be inserted.

	   # note single quotes to prevent interpolated of variables
	   $context->debugging( format => '## $file line $line: $text' );

       The final use of this method is to generate debugging messages themselves.  The first
       argument should be "msg", followed by a reference to a hash array of value to insert into
       the debugging format string.

	   $context->debugging(
	       msg => {
		   line => 20,
		   file => 'example.tt',
		   text => 'Trampoline! Trampoline!',
	       }
	   );

   AUTOLOAD
       An "AUTOLOAD" method provides access to context configuration items.

	   $stash     = $context->stash();
	   $tflag     = $context->trim();
	   $epflag    = $context->eval_perl();
	   ...

AUTHOR
       Andy Wardley <abw@wardley.org> <http://wardley.org/>

COPYRIGHT
       Copyright (C) 1996-2012 Andy Wardley.  All Rights Reserved.

       This module is free software; you can redistribute it and/or modify it under the same
       terms as Perl itself.

SEE ALSO
       Template, Template::Document, Template::Exception, Template::Filters, Template::Plugins,
       Template::Provider, Template::Service, Template::Stash

perl v5.16.3				    2012-01-25			     Template::Context(3)
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