Provided by: libtext-xslate-perl_3.5.9-1build1_amd64 
NAME
Text::Xslate::Manual::FAQ - Frequently asked questions and answers
DESCRIPTION
This manual page lists FAQs, which we've heard for now.
QUESTIONS
General
How do you pronounce 'Xslate'?
We read it "/eks-leit/".
What 'Xslate' stands for?
It stands for XS template, a template engine written in XS, although pure Perl
implementations are also provided.
What are 'Kolon', 'Metakolon', and 'TTerse' ?
Xslate supports multiple template syntaxes. Kolon is the default syntax, Metakolon is
suitable to output Kolon templates, and TTerse is compatible with Template-Toolkit 2. You
can specify the template syntax by passing "syntax" option to the Text::Xslate
constructor.
my $tx = Text::Xslate->new(
syntax => 'TTerse', # by moniker
);
my $tx = Text::Xslate->new(
syntax => 'Text::Xslate::Syntax::TTerse', # by fully qualified name
);
What version of perl does Xslate require?
Xslate is tested on perl v5.8.1. No special settings should be required.
How can I install the pure-Perl version of Xslate?
Pass "PUREPERL_ONLY=1" to Makefile.PL, which requests the Xslate build system not to make
XS parts.
Note that "cpanm 1.7" supports "--pp" option to install pure-Perl alternatives, so you can
type "cpanm --pp Text::Xslate".
What optimizations does Xslate employs?
Here are some optimizations worth noting that makes Text::Xslate run so fast, in no
particular order:
Pre-compiled templates
Text::Xslate is among the template engines that pre-compile the templates. This is
similar to, say, Template::Toolkit, but Text::Xslate compiles the templates to C
structures and stores them as binary data.
Built on top of a virtual machine
Text::Xslate is built on top of virtual machine that executes bytecode, and this
virtual machine is fine-tuned specifically for template processing.
The virtual machine also employs optimizations such as direct-threading style coding
to shave off any extra milliseconds that the engine might take otherwise
Custom byte codes for oft-used operations
Some operations which are used very often are optimized into its own byte code. For
example (as described elsewhere) Text::Xslate automatically escapes HTML unless you
tell it not to. Text::Xslate implements this process which involves escaping the
string while appending the result to the output buffer in C, as a custom byte code.
This lets you avoid the penalties usually involved in such operations.
Pre-allocation of output buffers
One of the main things to consider to reduce performance degradation while processing
a template is to avoid the number of calls to "malloc()". One of the tricks that
Text::Xslate employs to reduce the number of calls to "malloc()" is to pre-allocate
the output buffer in an intelligent manner: For example, Text::Xslate assumes that
most templates will be rendered to be about the same as the previous run, so when a
template is rendered it uses the size allocated for the previous rendering as an
approximation of how much space the current rendering will require. This allows you to
greatly reduce the number of "malloc()" calls required to render a template.
How can I throw errors in functions and/or methods?
Handle warnings by "warn_handler" and raises exceptions if needed.
That's because Xslate catches exceptions in templates and emits them as warnings.
Configuration
When should I create the Xslate instance?
Xslate instances are reusable and creating the instance costs somewhat so you're
recommended to reuse them as much as possible. That is, you should make the instance
global.
Consider a PSGI application:
# create Xslate here, not in psgi_app();
my $xslate = Text::Xslate->new(...);
sub psgi_app {
my($env) = @_;
# use $xslate and create $response
return $response;
}
return \&psgi_app; # as a PSGI app
Don't create the instance in each request. It's less efficient.
How can I change instance attributes dynamically?
Instance attributes, e.g. "include_path", "function", or "syntax", are immutable, so you
cannot change them dynamically.
Instead, you can create multiple instances by different options. instance in order to
avoid conflicts with cache directories.
For example:
my %common_config = ( cache_dir => $dir, module => \@module );
my %xslate = (
ja => Text::Xslate->new( path => [ $template_ja ], %common_config ),
en => Text::Xslate->new( path => [ $template_en ], %common_config ),
ro => Text::Xslate->new( path => [ $template_ro ], %common_config ),
);
$xslate{$lang}->render(...);
Templates
How can I changes template tags?
Use "start_tag", "end_tag", and "line_start" options to "new" method, which can be joined
together with "syntax" option:
my $tx = Text::Xslate->new(
syntax => 'TTerse',
tag_start => '{{',
tag_end => '}}',
line_start => undef,
);
print $tx->render_string('Hello, {{lang}} world!', { lang => 'Xslate' });
Note that you'd better to avoid symbols which can be used for operators.
How can I iterate over HASH references?
Convert HASH references into ARRAY references because "for" methods can deal with just
ARRAY references.
: # in Kolon
: # iterate $hash by keys
: for $hash.keys() -> $key {
<: $key :>
: }
: # by values
: for $hash.values() -> $value {
<: $value :>
: }
: # by key-value pairs
: for $hash.kv() -> $pair {
<: $pair.key :>=<: $pair.value :>
: }
Note that the above methods return ARRAY references sorted by the keys.
How can I use Template-Toolkit virtual methods and filters?
Xslate itself does not support these methods and filters, but there are modules on CPAN
that implement them.
Text::Xslate::Bridge::TT2 provides almost all the TT methods and filters, but it requires
Template-Toolkit installed.
Text::Xslate::Bridge::TT2Like provides the same features as "T::X::Bridge::TT2", and it
does not require the Template-Toolkit runtime.
These bridge modules are useful not only for TTerse users, but also for Kolon users.
How can I (write|get) plugins?
It is unlikely to need to write plugins for Xslate, because Xslate allows you to export
any functions to templates. Any function-based modules are available by the "module"
option.
Xslate also allows you to call methods for object instances, so you can use any object-
oriented modules, except for classes which only provide class methods (they need
wrappers).
If you want to add methods to builtin data types (nil, scalars, arrays and hashes), you
can write bridge modules. See Text::Xslate::Bridge for details.
How to limit while-loop like Template-Toolkit?
While Template-Toolkit has a loop counter to prevent runaway "WHILE" loop, Xslate has no
arbitrary limitation.
Instead, you can use "alarm()" to limit any runaway code:
eval {
local $SIG{ALRM} = sub { die @_ };
alarm(1); # set timeout
$tx->render('<: while true { } :>', \%vars);
};
if($@ =~ /\b ALRM \b/xms) {
# timeout!
}
Does Xslate process text strings, or binary strings?
(The meaning of text string and binary string is that of Perl, see perlunifaq.)
Xslate assumes template files to be encoded in "UTF-8" by default, so the output is a text
string and template parameters, including values which registered functions return, must
be text strings.
However, if you want to process binary strings, you can do so by passing ":bytes" to
"input_layer", although it's not recommended.
Why doesn't I cannot access $object.attr like TT2?
Template-Toolkit allows objects (i.e. blessed references) to access its element if the
object has no accessor methods, i.e. "[% object.attr %]" might mean "$object->{attr}".
This behavior breaks encapsulation and hides typos, so Xslate doesn't allow such
fallbacks.
If you want to access object attributes, define the accessors of them, or prepare values
as a non-object before calling "render()".
Can I load macros in other template files?
Not yet. Currently Xslate doesn't support external macros.
Functions, filters and macros
Where are the list of builtin functions?
See Text::Xslate::Manual::Builtin.
How can I use macros as a callback to high-level functions?
Macros are objects that overload "&{}", the CODE dereference operator, so all you have to
do is to call them simply, but don't check their types because they are not a real CODE
reference.
my $tx = Text::Xslate->new(
function => {
count => sub {
my($a, $cb) = @_;
# Don't check the type of $cb!
return scalar grep { $cb->($_) } @{$a};
},
},
);
print $tx->render_string('<: count($a, -> $x { $x >= 50 }) :>',
{ a => [ 0 .. 100 ] },
); # => 50
Web Application Frameworks
How can I use Xslate in $my_favorite_WAF?
There are bridges that integrate Xslate into WAFs:
• Catalyst::View::Xslate for Catalyst
• MojoX::Renderer::Xslate for Mojolicious
• Tiffany for general usage
There are WAFs which adopt Xslate as the default template engine:
• Amon2
• Pickles
Where are examples which use Xslate in Catalyst?
There is a real-world project that uses Xslate with Catalyst.
<https://github.com/duckduckgo/community-platform>
Initializing Xslate:
<https://github.com/duckduckgo/community-platform/blob/master/lib/DDGC.pm#L268>
Working on: <https://dukgo.com/>
Enjoy!
Development and support
How can I colorize Xslate templates?
For "vim" user, there is xslate.vim for Kolon:
<https://github.com/motemen/xslate-vim>
For "emacs" user, there are plugins:
<https://github.com/samvtran/kolon-mode>
<https://github.com/yoshiki/tx-mode>
Where can I ask questions?
The mailing list is recommended to ask questions.
<http://groups.google.com/group/xslate>
If you find a bug or have a request, creating github issues is better because those
tickets are less likely to disappear than the ports in the mailing list.
<https://github.com/xslate/p5-Text-Xslate/issues>
I found a bug! What can I do for you?
Please make a minimal test case to show the problem clearly. The code is the common
language both I and you speak fluently ;)
SEE ALSO
Text::Xslate
Text::Xslate::Manual
Text::Xslate::Manual::Cookbook