import vs import - iOS 7

Question

I am playing around with some of the new iOS 7 features and working with some of the Image Effects as discussed in the WWDC video  Implementing Engaging UI on iOS   For producing a blur effect within the source code for the session  UIImage was extended via a category which imports UIKit like so    import UIKit    I think I saw something about this in another session video but I m having trouble finding it  I m looking for any background information on when to use this  Can it only be used with Apple frameworks  Are the benefits of using this compiler directive enough that I should go back and update old code

User · Accepted Answer

It s a new feature called Modules or  quot semantic import quot   There s more info in the WWDC 2013 videos for Session 205 and 404  It s kind of a better implementation of the pre-compiled headers  You can use modules with any of the system frameworks in iOS 7 and Mavericks  Modules are a packaging together of the framework executable and its headers and are touted as being safer and more efficient than  import  One of the big advantages of using  import is that you don t need to add the framework in the project settings  it s done automatically  That means that you can skip the step where you click the plus button and search for the framework  golden toolbox   then move it to the  quot Frameworks quot  group  It will save many developers from the cryptic  quot Linker error quot  messages  You don t actually need to use the  import keyword  If you opt-in to using modules  all  import and  include directives are mapped to use  import automatically  That means that you don t have to change your source code  or the source code of libraries that you download from elsewhere   Supposedly using modules improves the build performance too  especially if you haven t been using PCHs well or if your project has many small source files  Modules are pre-built for most Apple frameworks  UIKit  MapKit  GameKit  etc   You can use them with frameworks you create yourself  they are created automatically if you create a Swift framework in Xcode  and you can manually create a  quot  modulemap quot  file yourself for any Apple or 3rd-party library  You can use code-completion to see the list of available frameworks   Modules are enabled by default in new projects in Xcode 5  To enable them in an older project  go into your project build settings  search for  quot Modules quot  and set  quot Enable Modules quot  to  quot YES quot   The  quot Link Frameworks quot  should be  quot YES quot  too   You have to be using Xcode 5 and the iOS 7 or Mavericks SDK  but you can still release for older OSs  say iOS 4 3 or whatever   Modules don t change how your code is built or any of the source code   From the WWDC slides    Imports complete semantic description of a framework Doesn t need to parse the headers Better way to import a framework   s interface Loads binary representation More flexible than precompiled headers Immune to effects of local macro definitions  e g   define readonly 0x01  Enabled for new projects by default    To explicitly use modules  Replace  import  lt Cocoa Cocoa h gt  with  import Cocoa  You can also import just one header with this notation   import iAd ADBannerView   The submodules autocomplete for you in Xcode

User · Answer

History   include   gt   import   gt   pch   gt   import    include vs  import     pch - Precompiled header  Module -  import Product Name    Product Module Name    import module declaration says to compiler to load a precompiled binary of framework which decrease a building time  Modular Framework contains  modulemap About  If module feature is enabled in Xcode project  include and  import directives are automatically converted to  import that brings all advantages

User · Answer

There is a few benefits of using modules  You can use it only with Apple s framework unless module map is created   import is a bit similar to pre-compiling headers files when added to  pch file which is a way to tune app the compilation process  Additionally you do not have to add libraries in the old way  using  import is much faster and efficient in fact  If you still look for a nice reference I will highly recommend you reading this article

User · Answer

It seems that since XCode 7 x a lot of warnings are coming out when enabling clang module with CLANG ENABLE MODULES  Take a look at Lots of warnings when building with Xcode 7 with 3rd party libraries

User · Answer

Nice answer you can find in book Learning Cocoa with Objective-C  ISBN  978-1-491-90139-7   Modules are a new means of including and linking files and libraries into your projects  To understand how modules work and what benefits they have  it is important to look back into the history of Objective-C and the  import statement Whenever you want to include a file for use  you will generally have some code that looks like this    import  someFile h    Or in the case of frameworks    import  lt SomeLibrary SomeFile h gt    Because Objective-C is a superset of the C programming language  the  import state- ment is a minor refinement upon C   s  include statement  The  include statement is very simple  it copies everything it finds in the included file into your code during compilation  This can sometimes cause significant problems  For example  imagine you have two header files  SomeFileA h and SomeFileB h  SomeFileA h includes SomeFileB h  and SomeFileB h includes SomeFileA h  This creates a loop  and can confuse the coimpiler  To deal with this  C programmers have to write guards against this type of event from occurring   When using  import  you don   t need to worry about this issue or write header guards to avoid it  However   import is still just a glorified copy-and-paste action  causing slow compilation time among a host of other smaller but still very dangerous issues  such as an included file overriding something you have declared elsewhere in your own code    Modules are an attempt to get around this  They are no longer a copy-and-paste into source code  but a serialised representation of the included files that can be imported into your source code only when and where they   re needed  By using modules  code will generally compile faster  and be safer than using either  include or  import   Returning to the previous example of importing a framework    import  lt SomeLibrary SomeFile h gt    To import this library as a module  the code would be changed to    import SomeLibrary    This has the added bonus of Xcode linking the SomeLibrary framework into the project automatically  Modules also allow you to only include the components you really need into your project  For example  if you want to use the AwesomeObject component in the AwesomeLibrary framework  normally you would have to import everything just to use the one piece  However  using modules  you can just import the specific object you want to use    import AwesomeLibrary AwesomeObject    For all new projects made in Xcode 5  modules are enabled by default  If you want to use modules in older projects  and you really should  they will have to be enabled in the project   s build settings  Once you do that  you can use both  import and  import statements in your code together without any concern

User · Answer

It currently only works for the built in system frameworks  If you use  import like apple still do importing the  UIKit framework in the app delegate it is replaced  if modules is on and its recognised as a system framework  and the compiler will remap it to be a module import and not an import of the header files anyway   So leaving the  import will be just the same as its converted to a module import where possible anyway

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