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GRMustache

GRMustache is an Objective-C implementation of the Mustache logic-less template engine.

It supports the following Mustache features:

  • comments
  • delimiter changes
  • variables
  • boolean sections
  • enumerable sections
  • inverted sections
  • lambda sections
  • partials and recursive partials

It supports extensions to the regular Mustache syntax:

Embedding in your XCode project

GRMustache is a standalone library made of the Objective-C files contained in the Classes folder. Just add them to your XCode project.

Import GRMustache.h in order to access all GRMustache features.

Header files whose names contain private declare private APIs which are subject to change, without notice, over releases.

Versioning

GRMustache versioning policy complies to the one defined by Apache APR.

Check the GRMustacheVersion.h header, and RELEASE_NOTES.md.

Testing

Open and build the GRMustache.xcodeproj project. If the build succeeds, all the tests pass!

You may also run the make command from the Terminal.

GRMustache is tested against the core, file_system, dot_key, and extended_path modules of the Mustache-Spec project. More tests come from the Ruby implementation.

Simple example

#import "GRMustache.h"

NSDictionary *object = [NSDictionary dictionaryWithObject:@"Mom" forKey:@"name"];
[GRMustacheTemplate renderObject:object fromString:@"Hi {{name}}!" error:nil];
// returns @"Hi Mom!"

Rendering methods

The main rendering methods provided by the GRMustacheTemplate class are:

// Renders the provided templateString.
+ (NSString *)renderObject:(id)object
                fromString:(NSString *)templateString
                     error:(NSError **)outError;

// Renders the template loaded from a url.
+ (NSString *)renderObject:(id)object
         fromContentsOfURL:(NSURL *)url
                     error:(NSError **)outError;

// Renders the template loaded from a bundle resource of extension "mustache".
+ (NSString *)renderObject:(id)object
              fromResource:(NSString *)name
                    bundle:(NSBundle *)bundle
                     error:(NSError **)outError;

// Renders the template loaded from a bundle resource of provided extension.
+ (NSString *)renderObject:(id)object
              fromResource:(NSString *)name
             withExtension:(NSString *)ext
                    bundle:(NSBundle *)bundle
                     error:(NSError **)outError;

All methods may return errors, described in the "Errors" section below.

Compiling templates

If you are planning to render the same template multiple times, it is more efficient to parse it once, with the compiling methods of the GRMustacheTemplate class:

// Parses the templateString.
+ (id)parseString:(NSString *)templateString
            error:(NSError **)outError;

// Loads and parses the template from url.
+ (id)parseContentsOfURL:(NSURL *)url
                   error:(NSError **)outError;

// Loads and parses the template from a bundle resource of extension "mustache".
+ (id)parseResource:(NSString *)name
             bundle:(NSBundle *)bundle
              error:(NSError **)outError;

// Loads and parses the template from a bundle resource of provided extension.
+ (id)parseResource:(NSString *)name
      withExtension:(NSString *)ext
             bundle:(NSBundle *)bundle
              error:(NSError **)outError;

Those methods return GRMustacheTemplate instances, which render objects with the following method:

- (NSString *)renderObject:(id)object;

For instance:

// Compile template
GRMustacheTemplate *template = [GRMustacheTemplate parseString:@"Hi {{name}}!" error:nil];
// @"Hi Mom!"
[template renderObject:[NSDictionary dictionaryWithObject:@"Mom" forKey:@"name"]];
// @"Hi Dad!"
[template renderObject:[NSDictionary dictionaryWithObject:@"Dad" forKey:@"name"]];
// @"Hi !"
[template renderObject:nil];
// @"Hi !", shortcut to renderObject:nil
[template render];

Context objects

You will provide a rendering method with a context object.

Mustache tag names are looked in the context object, through the standard Key-Value Coding method valueForKey:.

The most obvious objects which support KVC are dictionaries. You may also provide with any other object:

@interface Person: NSObject
+ (id)personWithName:(NSString *)name;
- (NSString *)name;
@end

// returns @"Hi Mom!"
[GRMustacheTemplate renderObject:[Person personWithName:@"Mom"]
                      fromString:@"Hi {{name}}!"
                           error:nil];

GRMustache catches NSUndefinedKeyException:

// doesn't throw, and returns @"Hi !"
[GRMustacheTemplate renderObject:[Person personWithName:@"Mom"]
                      fromString:@"Hi {{blame}}!"
                           error:nil];

Tag types

We'll now cover all mustache tag types, and how they are rendered.

But let's give some definitions first:

  • GRMustache considers enumerable all objects conforming to the NSFastEnumeration protocol, but NSDictionary. The most obvious enumerable is NSArray.

  • GRMustache considers false KVC key misses, and the following values: nil, [NSNull null], the empty string @"", and [GRNo no] which we'll see below in the "Booleans values" section.

Comments {{!...}}

Comments tags are not rendered.

Variable tags {{name}}

Such a tag is rendered according to the value for key name in the context.

If the value is false, the tag is not rendered.

Otherwise, it is rendered with the regular string description of the value, HTML escaped.

Unescaped variable tags {{{name}}} and {{&name}}

Such a tag is rendered according to the value for key name in the context.

If the value is false, the tag is not rendered.

Otherwise, it is rendered with the regular string description of the value, without HTML escaping.

Sections {{#name}}...{{/name}}

Sections are rendered differently, depending on the value for key name in the context:

False sections

If the value is false, the section is not rendered.

Enumerable sections

If the value is enumerable, the text between the {{#name}} and {{/name}} tags is rendered once for each item in the enumerable.

Each item becomes the context while being rendered. This is how you iterate over a collection of objects:

My shopping list:
{{#items}}
- {{name}}
{{/items}}

When a key is missed at the item level, it is looked into the enclosing context.

Lambda sections

If the value is a GRMustacheLambda, the section is rendered with the string returned by a block of code.

You will build a GRMustacheLambda with the GRMustacheLambdaMake function. This function takes a block which returns the string that should be rendered, as in the example below:

// A lambda which renders its section without any special effect:
GRMustacheLambda lambda = GRMustacheLambdaMake(^(GRMustacheRenderer renderer, id context, NSString *text) {
    return renderer(context);
});
  • renderer is a block which renders the inner section with its argument as a context.
  • context is the current rendering context.
  • text contains the litteral inner section, unrendered : {{tags}} will not have been expanded.

You may, for instance, implement caching:

__block NSString *cache = nil;
GRMustacheLambda cacheLambda = GRMustacheLambdaMake(^(GRMustacheRenderer renderer, id context, NSString *text) {
  if (cache == nil) { cache = renderer(context); }
  return cache;
});

You may also implement helper functions:

GRMustacheLambda linkLambda = GRMustacheLambdaMake(^(GRMustacheRenderer renderer, id context, NSString *text) {
  return [NSString stringWithFormat:
          @"<a href=\"%@\">%@</a>",
          [context valueForKey:@"url"], // url comes from current context
          renderer(context)]            // link text comes from the inner section
});

Other sections

Otherwise - if the value is not enumerable, false, or lambda - the content of the section is rendered once.

The value becomes the context while being rendered. This is how you traverse an object hierarchy:

{{#me}}
  {{#mother}}
    {{#father}}
      My mother's father was named {{name}}.
    {{/father}}
  {{/mother}}
{{/me}}

When a key is missed, it is looked into the enclosing context. This is the base mechanism for templates like:

{{! If there is a title, render it in a <h1> tag }}
{{#title}}
  <h1>{{title}}</h1>
{{/title}}

Inverted sections {{^name}}...{{/name}}

Such a section is rendered when the {{#name}}...{{/name}} section would not: in the case of false values, or empty enumerables.

Partials {{>partial_name}}

A {{>partial_name}} tag is rendered as a partial loaded from the file system.

Partials must have the same extension as their including template.

Recursive partials are possible. Just avoid infinite loops in your context objects.

Depending on the method which has been used to create the original template, partials will be looked in different places :

  • In the main bundle:
    • renderObject:fromString:error:
    • parseString:error:
  • In the specified bundle:
    • renderObject:fromResource:bundle:error:
    • renderObject:fromResource:withExtension:bundle:error:
    • parseResource:bundle:error:
    • parseResource:withExtension:bundle:error:
  • Relatively to the URL of the including template:
    • renderObject:fromContentsOfURL:error:
    • parseContentsOfURL:error:

The "Template loaders" section below will show you more partial loading GRMustache features.

Dot key and extended paths

Extended paths

GRMustache supports extended paths introduced by Handlebars.js. Paths are made up of typical expressions and / characters. Expressions allow you to not only display data from the current context, but to display data from contexts that are descendents and ancestors of the current context.

To display data from descendent contexts, use the / character. So, for example, if your context were structured like:

context = [NSDictionary dictionaryWithObjectsAndKeys:
           [Person personWithName:@"Alan"], @"person",
           [Company companyWithName:@"Acme"], @"company",
           nil];

you could display the person's name from the top-level context with the following expression:

{{person/name}}

Similarly, if already traversed into the person object you could still display the company's name with an expression like `{{../company/name}}, so:

{{#person}}{{name}} - {{../company/name}}{{/person}}

would render:

Alan - Acme

Dot key

Consistently with "..", the dot "." stands for the current context itself. This dot key can be useful when iterating a list of scalar objects. For instance, the following context:

context = [NSDictionary dictionaryWithObject:[NSArray arrayWithObjects: @"beer", @"ham", nil]
                                      forKey:@"item"];

renders:

<ul><li>beer</li><li>ham</li></ul>

when applied to the template:

<ul>{{#item}}<li>{{.}}</li>{{/item}}</ul>

Booleans Values

There are a few rules to follow to help GRMustache behave correctly regarding booleans:

  • Don't use [NSNumber numberWithBool:] for controlling boolean sections.
  • Use [GRNo no] and [GRYes yes] instead.
  • Declare your BOOL properties with the @property keyword.

We'll explain each rule below.

When good old NSNumber drops

[NSNumber numberWithBool:NO] is identical to [NSNumber numberWithInteger:0]. There is no way, provided with a NSNumber, to tell whether its a false boolean, or a zero integer.

In order to be consistent with implementations of {{ mustache }} in other languages, GRMustache treats [NSNumber numberWithBool:NO] as the zero number, and not as false.

That is why you should not use [NSNumber numberWithBool:] for controlling boolean sections.

Introducing GRYes and GRNo

GRMustache provides two singletons for you to use as explicit boolean objects, which you can put directly in your dictionary contexts:

// [GRYes yes] represents a true value
// [GRNo no] represents a false value

context = [NSDictionary dictionaryWithObjectsAndKeys:
           @"Michael Jackson", @"name",
           [GRYes yes], @"dead",
           nil];

BOOL properties

BOOL properties which have been declared with the @property keyword are handled by GRMustache:

@interface Person: NSObject
@property BOOL dead;
@property NSString *name;
@end

In the following template, GRMustache would process the dead boolean property as expected, and display "RIP" next to dead people only:

{{#persons}}
- {{name}} {{#dead}}(RIP){{/dead}}
{{/persons}}

If you declare a custom getter for your property, make sure you don't use it in the template:

@interface Person: NSObject
@property (getter=isDead) BOOL dead;
@end

{{person}}
  {{#dead}}Don't use the isDead getter in templates!{{/dead}}
{{/person}}

In-depth BOOL properties

Undeclared BOOL properties

Undeclared BOOL properties, that is to say: selectors implemented without corresponding @property in some @interface block, will be considered as numbers:

@interface Person: NSObject
- (BOOL)dead;   // will be considered as 0 and 1 integers
@end

Collateral damage: signed characters

All properties declared as signed character will be considered as booleans:

@interface Person: NSObject
@property char initial; // will be considered as boolean
@end

We thought that, besides BOOL, it would be pretty rare that you would use a value of such a type in a template. However, should this behavior annoy you, we provide a mechanism for having GRMustache behave strictly about boolean properties.

Boolean Strict Mode

Enter the boolean strict mode with the following statement:

[GRMustache setStrictBooleanMode:YES];

In strict boolean mode, signed char and BOOL properties will be considered as numbers.

The case for C99 bool

You may consider using the unbeloved C99 bool type:

@interface Person: NSObject
- (bool)dead;   // Works in and out of strict boolean mode
                // even without @property declaration
@end

Template loaders

Fine tuning loading of templates

The GRMustacheTemplateLoader class is able to load templates and their partials from anywhere in the file system, and provides more options than the high-level methods already seen.

You may instanciate one with the following GRMustacheTemplateLoader class methods:

// Loads templates and partials from a directory, with "mustache" extension, encoded in UTF8
+ (id)templateLoaderWithBaseURL:(NSURL *)url;

// Loads templates and partials from a directory, with provided extension, encoded in UTF8
+ (id)templateLoaderWithBaseURL:(NSURL *)url
                      extension:(NSString *)ext;

// Loads templates and partials from a directory, with provided extension, encoded in provided encoding
+ (id)templateLoaderWithBaseURL:(NSURL *)url
                      extension:(NSString *)ext
                       encoding:(NSStringEncoding)encoding;

// Loads templates and partials from a bundle, with "mustache" extension, encoded in UTF8
+ (id)templateLoaderWithBundle:(NSBundle *)bundle;

// Loads templates and partials from a bundle, with provided extension, encoded in UTF8
+ (id)templateLoaderWithBundle:(NSBundle *)bundle
                     extension:(NSString *)ext;

// Loads templates and partials from a bundle, with provided extension, encoded in provided encoding
+ (id)templateLoaderWithBundle:(NSBundle *)bundle
                     extension:(NSString *)ext
                      encoding:(NSStringEncoding)encoding;

Once you have a GRMustacheTemplateLoader object, you may load a template from its location:

GRMustacheTemplate *template = [loader parseTemplateNamed:@"document" error:nil];

You may also have the loader parse a template string. Only partials would then be loaded from the loader's location:

GRMustacheTemplate *template = [loader parseString:@"..." error:nil];

The rendering is done as usual:

NSString *rendering = [template renderObject:...];

Implementing your own template loading strategy

GRMustache is shipped with built-in ability to load templates and partials from the file system, or from a bundle, as seen above.

If this does not fit your needs, you may subclass the GRMustacheTemplateLoader class.

We provide below the implementation of a template loader which loads partials from a dictionary containing template strings:

#import "GRMustache.h"

@interface DictionaryTemplateLoader : GRMustacheTemplateLoader {
  NSDictionary *templatesByName;
}
+ (id)loaderWithDictionary:(NSDictionary *)templatesByName;
- (id)initWithDictionary:(NSDictionary *)templatesByName;
@end

// In your implementation file, import the GRMustacheTemplateLoader_protected.h
// header, dedicated to GRMustacheTemplateLoader subclasses:
#import "GRMustacheTemplateLoader_protected.h"

@implementation DictionaryTemplateLoader

+ (id)loaderWithDictionary:(NSDictionary *)templatesByName {
  return [[[self alloc] initWithDictionary:templatesByName] autorelease];
}

- (id)initWithDictionary:(NSDictionary *)theTemplatesByName {
  // initWithExtension:encoding: is the designated initializer.
  // provide it with some values, even if we won't use them.
  if (self == [self initWithExtension:nil encoding:NSUTF8StringEncoding]) {
    templatesByName = [theTemplatesByName retain];
  }
  return self;
}

- (void)dealloc {
  [templatesByName release];
  [super dealloc];
}

// This method must be implemented by GRMustacheTemplateLoader subclasses.
// Provided with a partial name, returns an object which uniquely identifies a template.
- (id)templateIdForTemplateNamed:(NSString *)name relativeToTemplateId:(id)baseTemplateId {
  return name;
}

// This method must be implemented by GRMustacheTemplateLoader subclasses.
// Returns a template string.
- (NSString *)templateStringForTemplateId:(id)templateId error:(NSError **)outError {
  return [templatesByName objectForKey:templateId];
}

@end

Now you may instanciate one:

DictionaryTemplateLoader *loader = [DictionaryTemplateLoader loaderWithDictionary:
                                    [NSDictionary dictionaryWithObject:@"It works!"
                                                                forKey:@"partial"]];

Then load a template from it:

GRMustacheTemplate *template = [loader parseString:@"{{>partial}}" error:nil];

And finally render:

[template render];  // "It works!"

Errors

The GRMustache library may return errors whose domain is GRMustacheErrorDomain.

extern NSString* const GRMustacheErrorDomain;

Their error codes may be interpreted with the GRMustacheErrorCode enumeration:

typedef enum {
    GRMustacheErrorCodeParseError,
    GRMustacheErrorCodeTemplateNotFound,
} GRMustacheErrorCode;

A less simple example

Let's be totally mad, and display a list of people and their birthdates in a UIWebView embedded in our iOS application.

We'll most certainly have a UIViewController for displaying the web view:

@interface PersonListViewController: UIViewController
@property (nonatomic, retain) NSArray *persons;
@property (nonatomic, retain) IBOutlet UIWebView *webView;
@end

The persons array contains some instances of our Person model:

@interface Person: NSObject
@property (nonatomic, retain) NSString *name;
@property (nonatomic, retain) NSDate *birthdate;
@end

A PersonListViewController instance and its array of persons is a graph of objects that is already perfectly suitable for rendering our template:

PersonListViewController.mustache:

<html>
<body>
<dl>
  {{#persons}}
  <dt>{{name}}</dt>
  <dd>{{localizedBirthdate}}</dd>
  {{/persons}}
</dl>
</body>
</html>

We already see the match between our classes' properties, and the persons and name keys. More on the birthdate vs. localizedBirthdate later.

We should already be able to render most of our template:

@implementation PersonListViewController
- (void)viewWillAppear:(BOOL)animated {
  // Let's use self as the rendering context:
  NSString *html = [GRMustacheTemplate renderObject:self
                                       fromResource:@"PersonListViewController"
                                       bundle:nil
                                       error:nil];
  [self.webView loadHTMLString:html baseURL:nil];
}
@end

Now our {{#persons}} enumerable section and {{name}} variable tag will perfectly render.

What about the {{localizedBirthdate}} tag?

Since we don't want to pollute our nice and clean Person model, let's add a category to it:

@interface Person(GRMustache)
@end

static NSDateFormatter *dateFormatter = nil;
@implementation Person(GRMustache)
- (NSString *)localizedBirthdate {
  if (dateFormatter == nil) {
    dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateStyle:NSDateFormatterLongStyle];
    [dateFormatter setTimeStyle:NSDateFormatterNoStyle];
  }
  return [dateFormatter stringFromDate:date];
}
@end

And we're ready to go!

License

Released under the MIT License

Copyright (c) 2010 Gwendal Roué

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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