For example, I have two files called file1.swift
and file2.swift
.
file1.swift
:
import UIKit class A: B { }
file2.swift
:
import UIKit class C: A{ }
I am reading that public class can not subclassed outside of module. Here I have subclass C. I am trying to understand what does module mean here. I imported to same module UIKit for both file. So the both files are of same module? So that I can subclassed. Or both files have different module even I import the same UIKit?
Can anybody explain what is module?
Source:
Classes with public access, or any more restrictive access level, can be subclassed only within the module where they’re defined.
Class members with public access, or any more restrictive access level, can be overridden by subclasses only within the module where they’re defined.
Module: A set of parts that can be assembled into a structure. To Xcode, that means you can have a group of lines of code that you can (re)use in different places without having to write that code again.
Internal: this means only your Swift code can read and write the property. If you ship your code as a framework for others to use, they won't be able to read the property. File Private: this means that only Swift code in the same file as the type can read and write the property.
In Swift 3 and swift 4, we have open, public, internal, fileprivate, and private for access control. Open access is the highest (least restrictive) access level and private access is the lowest (most restrictive) access level.
A module is a single unit of code distribution—a framework or application that is built and shipped as a single unit and that can be imported by another module with Swift’s import keyword.
Each build target (such as an app bundle or framework) in Xcode is treated as a separate module in Swift. If you group together aspects of your app’s code as a stand-alone framework—perhaps to encapsulate and reuse that code across multiple applications—then everything you define within that framework will be part of a separate module when it’s imported and used within an app, or when it’s used within another framework.
As the docs indicate, the module is an application or a framework (library). If you create a project with classes A
and B
, they are part of the same module. Any other class in the same project can inherit from those classes. If you however import that project to another project, classes from that another project won't be able to subclass A
nor B
. For that you would have to add open
indicator before their declarations.
Basically, if you work on a single app then you are working in one single module and unless declared as private
or fileprivate
, the classes can subclass each other.
EDIT
Let us have following class in module (project) Module1:
class A { }
Since this class is not open
, it can be subclassed only within the same module. That means that following class:
class B: A { }
Can be written only in the same project, in Module1.
If you add Module1 as a dependency to project Module2, and try to do this:
import Module1 class C: A { }
It will not compile. That's because class A
is not open
(in other words it has access public
or less) and it does not belong to the same module as C
. A
belongs to Module1, C
belongs to Module2.
Note
import
keyword imports a dependency module to your current module. If you write import UIKit
in your project, you are telling the compiler that you want to use module UIKit
in your module. import
does not define current module. Current module is the current project.
Adding import UIKit
at the beginning of the file does not change nor define to which module the file belongs. It just tells the compiler that in that file you want to use code from UIKit
module.
Swift module(.swiftmodule)
History:
#include => #import => Precompiled Headers .pch => @import Module(ObjC); => import Module(Swift)
[#include vs #import]
[Precompiled Headers .pch]
[@import Module(ObjC);]
There are two type of it
.swiftmodule
folder. Folder contains all .swiftmodule
files for architectures and other meta information like:
.swiftmodule
file. It is binary file format which contains Abstract Syntax Tree(AST) or Swift Intermediate Language(SIL) of framework's public API..swiftdoc
- attached docs which can be revived by consumer.swiftinterface
- Module stability[.swiftinterface or Swift Module Interfaces] is a next step of improving closed source compatibility
When you Jump to Definition
of imported module actually you reviewing public interface of .modulemap
Binary(library, framework) can contains several modules, each module can contains a kind of submodule(from Objective-C world) thought.
import struct SomeModule.SomeStruct
These modules can have dependencies between each others.
Also Module is a kind of scope which can help compiler to figure out which exactly class to use. If two modules use the same name you get
Ambiguous use of 'foo()'
It can be solved by:
import ModuleName1 import ModuleName2 func someFunc() { ModuleName1.SomeClass.foo() ModuleName2.SomeClass.foo() }
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With