Issue#972
We want to have a swifty UserDefaults API that works with subscript and in a type safe manner.
extensionDefaults.Keys{staticletstring=Defaults.Key("string",default:"0")}XCTAssertEqual(defaults[.string],"0")defaults[.string]="1"XCTAssertEqual(defaults[.string],"1")UserDefaults plist compatibility
DefineCompatible protocol that allows value to be plist compatible
The value parameter can be only property list objects: NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. For NSArray and NSDictionary objects, their contents must be property list objects.
publicprotocolCompatible:Equatable{}extensionInt:Compatible{}extensionString:Compatible{}extensionBool:Compatible{}extensionDate:Compatible{}extensionArray:CompatiblewhereElement:Compatible{}extensionDictionary:CompatiblewhereKey:Compatible,Value:Compatible{}Next, defineDefaults that acceptsUserDefaults as initialize dependency, so that we can swap UserDefaults.
Key with generic type
We defineKey with phantom typeValue so we know which value this key is pointing to, this makes it easier to reason about the code.
Since Swift has limitationStatic stored properties not supported in generic types, we can’t extend ourKey with static stored properties, we have to do via computed property
extensionDefaults.Key{staticvarstring:Defaults.Key<String>{.init("string",default:"0")}}This works, but does not look nice. To workaround this, we define classAnyKey and make ourKey class as well and inherited thisAnyKey class.
Make a typealiastypealias Keys = AnyKey so we can refer toDefaults.Keys when we define our keys.
publicclassDefaults{publicvarsuite:UserDefaultspublicinit(suite:UserDefaults=.standard){self.suite=suite}publicsubscript<Value:Compatible>(key:Key<Value>)->Value{get{ifletvalue=suite.object(forKey:key.name)as?Value{returnvalue}returnkey.defaultValue}set{suite.set(newValue,forKey:key.name)}}publicfuncexists<Value:Compatible>(key:Key<Value>)->Bool{suite.object(forKey:key.name)!=nil}}extensionDefaults{publictypealiasKeys=AnyKeypublicclassKey<Value:Compatible>:AnyKey{vardefaultValue:Valuepublicinit(_name:String,defaultdefaultValue:Value){self.defaultValue=defaultValuesuper.init(name:name)}}publicclassAnyKey{varname:Stringinit(name:String){self.name=name}}}extensionDefaults.AnyKey:Equatable{publicstaticfunc==(lhs:Defaults.AnyKey,rhs:Defaults.AnyKey)->Bool{lhs.name==rhs.name}}extensionDefaults.AnyKey:Hashable{publicfunchash(intohasher:inoutHasher){hasher.combine(name)}}How about Optional
We can supportOptional as well, as long as it’s underlying value is compatible. Since the type is defined viaKey, we can’t accidentally use Optional when the Key has non Optional value
extensionOptional:CompatiblewhereWrapped:Compatible{}extensionDefaults{publicsubscript<Value:Compatible>(key:Key<Optional<Value>>)->Value?{get{ifletvalue=suite.object(forKey:key.name)as?Value{returnvalue}returnnil}set{ifletnewValue{suite.set(newValue,forKey:key.name)}else{suite.removeObject(forKey:key.name)}}}}extensionDefaults.Keys{staticletoptional=Defaults.Key<Int?>("optional.int",default:nil)}functestOptional(){XCTAssertNil(defaults[.optional])defaults[.optional]=1XCTAssertEqual(defaults[.optional],1)defaults[.optional]=nilXCTAssertNil(defaults[.optional])}Start the conversation
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