swift - make init() private for NSObject subclass -

the class fooclass should allow interaction via sharedinstance. trying prevent misuse not allowing access init() of fooclass.

i have tried few different approaches, none work:

using private keyword:

class fooclass: nsobject {     // singleton     static let sharedinstance = fooclass()      let value: string      private override init() {         self.value = "asdf"     } }  // should compile error, not let foo = fooclass() 

using @available:

class fooclass: nsobject {     // singleton     // compile error - "init unavailable. use sharedinstance"     static let sharedinstance = fooclass()      let value: string      @available(*, unavailable, message="use sharedinstance")     override init() {         self.value = "asdf"     } }  // compile error - should let foo = fooclass() 

i have tried using internal well, still no luck.

update

first version works if move own file, objc version of class still allows init called. ideas?

swift_class("_ttc11swifttoobjc8fooclass") @interface fooclass : nsobject + (fooclass * __nonnull)sharedinstance; @property (nonatomic, readonly, copy) nsstring * __nonnull value; - (nonnull instancetype)init objc_designated_initializer; @end 

this answer addresses swift 2. in swift 3 looks access level of method correctly imported swift objective-c , not need marked ns_unavailable in order disallow being available. of course, there no new method in swift still need marked ns_unavailable maintain singleton properly.

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your first approach work long class put in own file. access control keyword private means defined feature available within containing file.

however, said, using swift class in objective-c remove protection private gives you. believe that's because marked private not have entry in imported header file generated compiler. init function inherited nsobject available because isn't overridden.

the solution found create header file explicitly declares init function can't called.

swift class:

@objc(fooclass) class fooclass: nsobject {   // singleton   static let sharedinstance = fooclass()    let value: string    private override init() {     self.value = "asdf"   } } 

objective-c header:

@interface fooclass (sharedinstance) + (instancetype) new  ns_unavailable; - (instancetype) init ns_unavailable; @end 

you have block new because if don't instance of class created through it.

testing:

fooclass* foo  = [fooclass sharedinstance]; // here fooclass* foo2 = [[fooclass alloc] init];   // 'init' unavailable fooclass* foo3 = [fooclass new];            // 'new' unavailable 

i have rudimentary example project here: sharedinstance project git