How can I make protected (like in ruby) variable or function in Swift? I know Swift has only 3 levels but nonetheless is it possible?
Access Levels
Swift provides three different access levels for entities within your
code. These access levels are relative to the source file in which an
entity is defined, and also relative to the module that source file
belongs to.
Public access enables entities to be used within any source file from
their defining module, and also in a source file from another module
that imports the defining module. You typically use public access when
specifying the public interface to a framework.
Internal access
enables entities to be used within any source file from their defining
module, but not in any source file outside of that module. You
typically use internal access when defining an app’s or a framework’s
internal structure.
Private access restricts the use of an entity to
its own defining source file. Use private access to hide the
implementation details of a specific piece of functionality.
Public
access is the highest (least restrictive) access level and private
access is the lowest (or most restrictive) access level
Currently I see only one solution - write parent class with private modifier and children class in single file but it's kind of painful.
Swift prefers to not use protected. You can read the reasons here Access Control and protected
In contrast, protected conflates access with inheritance, adding an entirely new control axis to reason about. It doesn’t actually offer any real protection, since a subclass can always expose “protected” API through a new public method or property. It doesn’t offer additional optimization opportunities either, since new overrides can come from anywhere. And it’s unnecessarily restrictive — it allows subclasses, but not any of the subclass’s helpers, to access something.
In Ruby's point of view, it may be important. However in Swift, neither it is useless, nor it is a matter of the language.
Swift language is primarily based on modules when it comes to access levels. It even has public private(set) variables, which is much needed in Objective-C (causes boilerplate).
There's no equivalent to protected in Swift where only subclasses have access to the method. Personally, I don't miss it.
In Swift (as Objective-C) there is far less emphasis on subclassing than other languages. If you find you have a set of methods that you want to be protected, it is probably better to factor them out as a delegate.
Swift 3.0 not cantains protected modifier. In our sdk we use internal(set) modifier that approve set operation only in sdk project.
private var _authorized : Bool = false
public internal(set) var authorized : Bool
{
get
{
return _authorized;
}
set
{
_authorized = newValue
}
}
Related
I have a DataManager class and it has some relevant functions and variables. For example,
Class DataManager: NSObject {
func doSomething()
func doSomethingAgain()
}
I move few method to an extension of DataManager. I made the extension as fileprivate cause I don't want to expose those function to other classes. For example,
Class DataManager: NSObject {
func doSomething()
}
fileprivate extension DataManager {
func doSomethingAgain()
}
Till now everything was fine, now the problem I am facing is when I am moving that extension to a different file that time fileprivate won't work. So what should be the protection level in that case. Hope you understood my intension.
The protection level should be internal (which is the default). It will then be available to everything in the module.
If you want to constrain access to a smaller number of classes, then you need to put those classes in their own module. Those are only access levels that Swift has.
The tightest access mode you can work with is the internal which is default in Swift.
Taking from https://docs.swift.org/swift-book/LanguageGuide/AccessControl.html :
"Swift provides five different access levels for entities within your code. These access levels are relative to the source file in which an entity is defined, and also relative to the module that source file belongs to.
Open access and public access enable entities to be used within any source file from their defining module, and also in a source file from another module that imports the defining module. You typically use open or public access when specifying the public interface to a framework. The difference between open and public access is described below.
Internal access enables entities to be used within any source file from their defining module, but not in any source file outside of that module. You typically use internal access when defining an app’s or a framework’s internal structure.
File-private access restricts the use of an entity to its own defining source file. Use file-private access to hide the implementation details of a specific piece of functionality when those details are used within an entire file.
Private access restricts the use of an entity to the enclosing declaration, and to extensions of that declaration that are in the same file. Use private access to hide the implementation details of a specific piece of functionality when those details are used only within a single declaration."
Swift offers 5 access modifiers: open, public, internal, fileprivate and private.
Of what I know about these specifiers, (mainly from link & link_2)
open means classes and class members can be subclassed and overridden both within and outside the defining module (target).
fileprivate restricts the use of an entity to its defining source file. Basically accessible by multiple classes within a single file.
private restricts the use of an entity to its enclosing declaration.
Now, public and internal seems pretty much the same to me :-
public means classes and class members can only be subclassed and overridden within the defining module (target).
internal enables an entity to be used within the defining module (target). Also, this happens to be the default specifier if nothing else is mentioned. We would typically use internal access when defining an app’s or a framework’s internal structure.
So basically how do public and internal differ?
This is my first Question here, so if I have missed out any details, please let me know. Thanks in advance.
Whatever you marked as public can be use within your app and outside of you app(module). If you marked something as internal that can only be used within your app(module). This is very helpful when your developing a library (framework) , you can use internal to hide library structure.
And Public members of A.swift and B.swift are available to C.swift and D.swift. The only restriction is that classes can't be subclassed (they would need to be open.)
- My answer base on #Keaz & #Alexander.
From Access Control manual:
Open access and public access enable entities to be used within any
source file from their defining module, and also in a source file from
another module that imports the defining module. You typically use
open or public access when specifying the public interface to a
framework. The difference between open and public access is described
below.
Internal access enables entities to be used within any source
file from their defining module, but not in any source file outside of
that module. You typically use internal access when defining an app’s
or a framework’s internal structure.
Difference is in visibility to other modules.
EDIT to answer #iCode comment:
You don't need all of them.
For simplest small single-dev application just using default internal will be enough.
If you will need to do it right you may add fileprivate/private accessors to hide some implementation.
If you're developing large app and want to separate code into modules, or if you're developing library you will need to use public/open to create inter-module interface.
I'm confused about the internal and private access modifier.
The docs says:
“Internal access enables entities to be used within any source file
from their defining module, but not in any source file outside of that
module. You typically use internal access when defining an app’s or a
framework’s internal structure.”
How I thought it was, was that with internal you can access everything if you are in your own app. But this is not true, because when I have a viewcontroller what is default internal and I'm having a internal function on that viewcontroller I can't access this from another file in another group (You create these in xCode).
What I tried was having a ViewController that has a method foo in group A then in group B I created a ViewController like this:
let vc: FakeViewController = FakeViewController()
vc.foo()
So is internal restricted to the same group? Or I'm I interpreting it wrong?
Is it useful that in a viewcontroller you create private methods and vars/lets?
#user1007522 Could you post the entire source code for FakeViewController? You should have access to foo() from your vc variable. If you do not, I suspect something else is in play here.
I found the following definitions much easier to understand (copied from UseYourLoaf - Swift 4 Access Levels)
The Five Access Levels of Swift 3/4
Swift 3 has five access levels that control from which source file or module you can access something. In order from most open to most restricted:
open you can access open classes and class members from any source file in the defining module or any module that imports that module. You can subclass an open class or override an open class member both within their defining module and any module that imports that module.
public allows the same access as open - any source file in any module - but has more restrictive subclassing and overriding. You can only subclass a public class within the same module. A public class member can only be overriden by subclasses in the same module. This is important if you are writing a framework. If you want a user of that framework to be able to subclass a class or override a method you must make it open.
internal allows use from any source file in the defining module but not from outside that module. This is generally the default access level.
fileprivate allows use only within the defining source file.
private Swift 4: allows use only from the enclosing declaration and new in Swift 4, to any extensions of that declaration in the same source file Swift 3: allows use only from the enclosing declaration.
Suppose you have 3 different view controller source files A, B, C
then
In Private:- If Intancses in A are Private than only A's Methods can use them
In Internal :- IF A is as Internal than B and C can easily use them.
Here is an example:
Thanks
Internal access restricts access to the files within a singular application or framework.
Private restricts access to the individual source file that your object is created in.
See this link for a more in-depth explanation.
Overall, if your "Group A" and "Group B" are in the same application or framework, you should be able to access the methods from each, assuming the viewController allows internal access.
My understanding is that private won't allow the variable from being accessed from outside that class. However, there are times, like with gesture recognizers, you can't make them private because they are needed behind the scenes. Marking them as "internal" lets them be accessed from within other functions, but not called directly.
Mostly I use internal to keep my code organized, so I know that's not a public facing function but it can still be used.
I had convenience methods littered all over the place. I have now pushed these in to a couple of helper classes and I made the helper classes protected members of my layer supertypes.
Everything was going along swimmingly until I came to Zend View. I have extended Zend View to make my layer supertype but when I try to attach a protected member it throws a:
Zend View Exception: Setting private or protected class members is not
allowed.
Firstly, why would such members not be allowed? Any ideas? Secondly, have you circumvented it in the past? And how did that go? (It seems that the framework detects protected members by the presence of a leading underscore. This seems a bit hit-and-miss, and also easy to get around).
Note - I'm not saying that I would circumvent it. I'm just trying to find out what others have done in the past (since it seems an odd constraint).
It's an important point for me since I am using traits to bring the helpers and associated proxy methods into each superclass. I don't want to maintain a separate trait just for the View. Alternatively, I don't want to make the helpers public members of each superclass.
Thank you!
Data encapsulation.
Underscore properties are not allowed primarily so that the developer can't accidentally overwrite View properties that are part of the framework.
This essentially protects all of the framework's View properties and allows you, the developer, free rain over any public properties you wish to set.
The authors of Zend View can then be sure of two things: (1) they control (and author) the private and protected class properties and (2) you control the public properties. This makes for logical data encapsulation and maintainable class overloading.
OK so I understand that ion VB6, encapsulated properties in a class can belong to one of three categories:
Public Property
Friend
Public Variable
What is the difference between these and how do these compare to public and private properties in a more modern language like C#?
The scope qualifiers Public and Friend determine whether clients in different projects can see the item.
Public items will be accessible to client code in other projects1 and code in the same project.
Friend items are accessible only to code in the same project, not to code in other projects.
Private items are accessible only to code in the same class.
Properties are different from public variables, because with properties you can execute your own code when the client gets or sets the value2. EDIT following Deanna's comment: Also note that variables can be passed ByRef to a function and changes will work as expected. This is NOT the case for properties.
NB C# may be more modern, but IMHO the VB6 treatment of properties and public variables is significantly better than the .Net treatment.
In VB6 you can change a public variable into a property without breaking the clients. You don't even have to recompile them. Not true in .Net.
In VB6 public variables can be used with data binding. Not true in .Net.
In VB6 public variables could be used with interfaces. Not true in .Net.
IMHO Microsoft made a real design mistake in creating these differences between properties and public fields in .Net. Not convinced? After the first releases of .Net, the C# and VB compilers were modified to support automatically implemented properties. These allow you to create properties in just one line of code, so that it's later possible to add logic on get/set without causing problems. IMHO this proves that public variables should have been made indistinguishable from properties.
1 Assuming your project type actually allows your classes to be used by other projects (i.e. ActiveX DLL, OCX, or ActiveX exe).
2 In the Property Get, Property Let and Property Set procedures.
Public means that it is accessible by any other classes that
references your project/dll.
Friend means that it is accessible by
any other classes within your assembly (so only the exe you made the
class in)
variable and property are almost the same. Property is preferred since you can set if other classes can set or get the variable (Property encapsulates the variable)
In C# it is the same, only you use Internal instead of Friend
private property are those property that are used by ourselves and other family member. But, public property are those property which are used by all the people of our community, society or the country.