When i declare a class:
class foo {
//code goes here
}
Is the class standard public, private or internal?
I was wondering about this and wasn't able to find any information about it.
According to the documentation :
All entities in your code (with a few specific exceptions, as
described later in this chapter) have a default access level of
internal if you do not specify an explicit access level yourself. As a
result, in many cases you do not need to specify an explicit access
level in your code
it is internal.
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 have some swift extensions I want to across projects.
I'd like to avoid category pollution though, unless those extensions are requested.
Is it possible to write them so that they only apply if I've done a certain import, like:
import MySwiftExtensions
// Use custom extensions
let x = [1,3,5,7].average()
let y = [1,3,5,7].firstWhere { $0 > 3 }
let z = "campervan".make1337()
I could write these as static methods wrapped in a single letter class (eg: ø.average([1,3,5,7]), like lodash) to achieve the same thing but sometimes you get much more concise usage from instance methods.
You wrote:
I have some swift extensions I want to across projects...
When I have code that I want to use across projects I create a separate framework to hold that code. Then, when I want to use that code in a new project, I embed the framework in that project. Or, for development purposes, I create a workspace that includes the project and the framework. That allows me to work on both at the same time, and then only embed the framework in the final product when it is time to export it.
Once the framework is either embedded or in the same workspace, then you should be able to import it into any individual file in your project with:
import MySwiftExtensions
Any file that does not have the import statement will not have access to the extensions.
EDIT:
Here is a link to a blog that describes how to create a Cocoa Touch Framework. And here is another link that describes in detail how to use workspaces to use frameworks in development projects.
I would like to focus attention on what you reported: "..only apply if I've done a certain import.."
It would also mean you want these extensions can be applyed only to a specific class
As reported in this interesting Apple blog chapter and in the official Apple doc you can handle the "Access Control" of your extension
You can extend a class, structure, or enumeration in any access
context in which the class, structure, or enumeration is available.
Any type members added in an extension have the same default access
level as type members declared in the original type being extended. If
you extend a public or internal type, any new type members you add
will have a default access level of internal. If you extend a private
type, any new type members you add will have a default access level of
private.
Alternatively, you can mark an extension with an explicit access level
modifier (for example, private extension) to set a new default access
level for all members defined within the extension. This new default
can still be overridden within the extension for individual type
members.
/* no access level modifier: default access level will be 'internal' */
extension UIViewSubClass
{
// default access level used: internal
var helloWorld : String {
get {
return "helloWorld"
}
}
}
// modify default access level to public
public extension UIViewSubClass
{
// default access level used: public
var helloWorld : String {
get {
return "helloWorld"
}
}
}
The members of extensions marked private are available within the file where they’re defined, and are not available outside that file. Outside the file where the private extension members were defined, any attempt to use them results in an error, and auto-complete wouldn’t even list them
// modify default access level to private
private extension UIViewSubClass
{
var helloWorld : String {
get {
return "helloWorld"
}
}
}
I don't believe you can do what you want per se, but I've used the following approach to provide functionality to only the specific class that implements an interface:
protocol ExampleProtocol {
}
extension ExampleProtocol where Self: UIViewController{
// extend what you need to here
}
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
}
}
Do you always create these two abstract base classes as the basis of any new project in DDD?
I've read that Entity should have two things. First, an identity property, probably of a generic type. Second, an Equals() method that determines whether it's the same as another Entity. Anything else? Any other natural methods or rules of thumb?
I like to have a common abstract ancestor for all my Domain objects but that is a matter of preference and overall infrastructure requirements.
After that, yes I have abstract classes for Entity and Value objects.
Don't forget that also overriding Equals for Value objects to return equality based on equal property state can be important.
Also people frequently overlook the value of packages. Put all these core base classes in their own "kernel" library and don't be reluctant to split your domain model into multiple assemblies instead of winding up with a single large "Domain Library".
If you're using .NET/C#, I've published a set of DDD interfaces and classes for public use. Take a look to see what typically goes inside them. The embedded code comments should hint towards their usage.
You can [download it here][1]. Project is dead now.
I've never needed the Equals() method in my applications thus far. Your mileage may vary though.
However, I create empty interfaces and use them as descriptors:
public interface IAggregateRoot {}
public interface IEntity {}
public interface IValueObject {}
public class Order : IAggregateRoot
{
...
}
public class State : IValueObject
{
...
}