Template::Context
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 represent-
ing 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 plu-
gins and filters, raise exceptions and so on.
A default "Template::Context" object is created by the Template mod-
ule. Any "Template::Context" options may be passed to the Template
new() constructor method and will be forwarded to the "Template::Con-
text" 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 con-
figuration parameters onto other default objects (e.g. Tem-
plate::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 instanti-
ated and passed to the Template new() constructor method as the "CON-
TEXT" 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::Con-
fig::CONTEXT package variable may be set to specify an alternate con-
text module. This will be loaded automatically and its new() construc-
tor method called by the context() factory method when a default con-
text 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 "Tem-
plate::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::Con-
text::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 Tem-
plate::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({ ... }),
},
});
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 vari-
ables.
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 com-
pletes.
$output = $context->include(’header’, { title => ’Hello World’ });
throw($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 Tem-
plate::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::Excep-
tion 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, $block)
Adds a new block definition to the internal BLOCKS cache. The first
argument should contain the name of the block and the second a refer-
ence to a Template::Document object or template sub-routine, or tem-
plate text which is automatically compiled into a template sub-rou-
tine.
Returns a true value (the sub-routine or Template::Document reference)
on success or undef on failure. The relevant error message can be
retrieved by calling the error() method.
define_filter($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.
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 subse-
quently delivered on request.
leave()
Compliment to the visit() method. Called by Template::Document objects
immediately after they process their content.
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.
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) 1996-2007 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, Tem-
plate::Stash
perl v5.8.8 2007-05-29 Template::Context(3)
