Name: plank
Owner: Pinterest
Description: A tool for generating immutable model objects
Created: 2017-02-14 23:06:42.0
Updated: 2018-01-11 14:52:13.0
Pushed: 2018-01-17 18:20:34.0
Homepage: https://pinterest.github.io/plank/
Size: 4889
Language: Swift
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Plank is a command-line tool for generating robust immutable Objective-C models from JSON Schemas. It will save you time writing boilerplate and eliminate model errors as your application scales in complexity.
Models are defined in JSON, a well-defined, extensible and language-independent specification.
Model classes are generated to be immutable. Each class provides a ?Builder? class to handle mutation.
Based on the type information specified in the schema definition, each class provides type validation and null reference checks to ensure model integrity.
ew install plank
Plank supports building in Ubuntu Linux via Docker. The Dockerfile in the repository will fetch the most recent release of plank and build dependencies including the Swift snapshot.
cker build -t plank .
Plank is built using the Swift Package Manager. Although you?ll be able to build Plank using swift build directly, for distribution of the binary we?d recommend using the commands in the Makefile since they will pass the necessary flags to bundle the Swift runtime.
ke archive
Keep reading to learn about Plank?s features or get your feet wet with the tutorial.
Plank takes a schema file as an input. Schemas are based on JSON, a well-defined, extensible and language-independent specification. Defining schemas in JSON allowed us to avoid writing unnecessary parser code and opened up the possibility of generating code from the same type system used on the server.
"id": "pin.json",
"title": "pin",
"description" : "Schema definition of a Pin",
"$schema": "http://json-schema.org/schema#",
"type": "object",
"properties": {
"id": { "type": "string" },
"link": { "type": "string", "format": "uri"}
}
You?ll notice we specify the name of the model and a list of its properties. Note that link specifies an additional format attribute which tells Plank to use a more concrete type like NSURL or NSDate.
Generate a schema file (pin.json) using Plank using the format plank [options] file1 file2 file3 ...
ank pin.json
This will generate files (Pin.h, Pin.m) in the current directory:
json Pin.h Pin.m
Learn more about usage on the installation page.
Plank will generate the necessary header and implementation file for your schema definition. Here is the output of the Pin.h header.
erface Pin
perty (nonatomic, copy, readonly) NSString *identifier;
perty (nonatomic, strong, readonly) NSURL *link;
All properties are readonly, as this makes the class immutable. Populating instances of your model with values is performed by builder classes.
Model mutations are performed through a builder class. The builder class is a separate type which contains readwrite properties and a build method that will create a new object. Here is the header of the builder that Plank generated for the Pin model:
erface PinBuilder
perty (nonatomic, copy, readwrite) NSString *identifier;
perty (nonatomic, strong, readwrite) NSURL *link;
in *)build;
erface Pin (BuilderAdditions)
nstancetype)initWithBuilder:(PinBuilder *)builder;
Plank will create an initializer method called initWithModelDictionary: that handles parsing NSDictionary objects that conform to your schema. The generated implementation will perform validation checks based on the schema?s types, avoiding the dreaded [NSNull null] showing up in your objects:
erface Pin (JSON)
nstancetype)initWithModelDictionary:(NSDictionary *)dictionary;
All Plank generated models implement methods to conform to NSSecureCoding, providing native serialization support out of the box.
OOL)supportsSecureCoding {
return YES;
nstancetype)initWithCoder:(NSCoder *)aDecoder {
if (!(self = [super init])) { return self; }
_identifier = [aDecoder decodeObjectOfClass:[NSString class] forKey:@"identifier"];
_link = [aDecoder decodeObjectOfClass:[NSURL class] forKey:@"link"];
return self;
oid)encodeWithCoder:(NSCoder *)aCoder {
[aCoder encodeObject:self.identifier forKey:@"identifier"];
[aCoder encodeObject:self.link forKey:@"link"];
With this implementation objects are serialized using NSKeyedArchiver:
reate a pin from a server response
*pin = [[Pin alloc] initWithModelDictionary:/* server response */];
ache the pin
eyedArchiver archiveRootObject:pin toFile:/* cached pin path */];
pp goes on, terminates, restarts...
oad the cached object
*cachedPin = [NSKeyedUnarchiver unarchiveObjectWithFile:/* cached pin path */];
Plank models support merging and partial object materialization through a conventional ?last writer wins? approach. By calling the mergeWithModel: on a generated model with a newer instance, the properties set on the newer instance will be preserved. To know which properties are set, the information is tracked internally within the model during initialization or through any mutation methods. In this example, an identifier property is used as a primary key for object equality:
ic inline id valueOrNil(NSDictionary *dict, NSString *key);
ct PinSetProperties {
signed int Identifier:1;
signed int Link:1;
nstancetype)initWithModelDictionary:(NSDictionary *)modelDictionary {
odelDictionary enumerateKeysAndObjectsUsingBlock:^(NSString * _Nonnull key, id obj, BOOL *stop){
if ([key isEqualToString:@"identifier"]) {
// ... Set self.identifier
self->_pinSetProperties.Identifier = 1;
}
if ([key isEqualToString:@"link"]) {
// ... Set self.link
self->_pinSetProperties.Link = 1;
}
;
Post notification
NSNotificationCenter defaultCenter] postNotificationName:@"kPlankModelDidInitializeNotification" object:self];
With immutable models, you have to think through how data flows through your application and how to keep a consistent state. At the end of every model class initializer, there?s a notification posted with the updated model. This is useful for integrating with your data consistency framework. With this you can track whenever a model has updated and can use internal tracking to merge the new model.
lementation Pin(ModelMerge)
nstancetype)mergeWithModel:(Pin *)modelObject {
PinBuilder *builder = [[PinBuilder alloc] initWithModelObject:self];
if (modelObject.pinSetProperties.Identifier) {
builder.identifier = modelObject.identifier;
}
if (modelObject.pinSetProperties.Link) {
builder.link = modelObject.link;
}
return [builder build];
Plank provides support for specifying multiple model types in a single property, commonly referred to as an Algebraic Data Type (ADT). In this example, the Pin schema receives an attribution property that will be either a User, Board, or Interest. Assume we have separate schemas defined in files user.json, board.json and interest.json, respectively.
"title": "pin",
"properties": {
"identifier": { "type": "string" },
"link": { "type": "string", "format": "uri"},
"attribution": {
"oneOf": [
{ "$ref": "user.json" },
{ "$ref": "board.json" },
{ "$ref": "interest.json" }
]
}
}
Plank takes this definition of attribution and creates the necessary boilerplate code to handle each possibility. It also provides additional type-safety by generating a new class to represent your ADT.
erface PinAttribution : NSObject<NSCopying, NSSecureCoding>
nstancetype)objectWithUser:(User *)user;
nstancetype)objectWithBoard:(Board *)board;
nstancetype)objectWithInterest:(Interest *)interest;
oid)matchUser:(void (^)(User * pin))userMatchHandler
orBoard:(void (^)(Board * board))boardMatchHandler
orInterest:(void (^)(Interest * interest))interestMatchHandler;
Note there?s a ?match? function declared in the header. This is how you extract the true underlying value of your ADT instance. This approach guarantees at compile-time you have explicitly handled every possible case preventing bugs and reducing the needs to use runtime reflection which hinders performance. The example below shows how you?d use this match function.
ttribution *attribution;
ribution matchUser:^(User *user) {
/ Do something with "user"
Board:^(Board *board) {
/ Do something with "board"
Interest:^(Interest *interest) {
/ Do something with "interest"
Pull requests for bug fixes and features welcomed.
Copyright 2017 Pinterest, Inc.
Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.