Objective-C: Do non-imported classes get compiled and linked into final binary? - objective-c

Question

In Objective-C, do all source files in the project get compiled and linked into the final binary even if they are not imported by any classes?

Answer 1

That depends on your target settings. If you go to the target's Build Phases, anything listed under Compile Sources will be compiled.

Answer 2

If the source file is part of the build then its classes end up in the binary and available at runtime. That's because the runtime is reflective and can be queried later to find them. The compiler cannot be certain that won't happen.
EDIT: a classic use case is an informal protocol. You may write code like:
- (void)initWithObject:(id)object
{
self = [super init];
if(self)
{
_title = [object title];
_value = [object value];
}
return self;
}
Then you might decide you want to add an implementation of that informal protocol to e.g. NSString:
#interface NSString (MYPropertyProtocol)
#end
#implementation NSString (MYPropertyProtocol)
- (NSString *)title
{
return #"Content";
}
- (NSString *)value
{
return self;
}
#end
Just because nobody imports the NSString category doesn't mean the methods aren't used.
Going beyond that, in my current app we have a protocol like (this is a heavily cut-down version):
#protocol MYTableViewCell
+ (NSArray *)acceptedObjectClasses;
- (void)setObject:(id)object;
#end
Subsequently UITableView subclasses can opt to implement MYTableViewCell. If so they are found automatically by traversing objc_getClassList (and a lot of caching) and used automatically by my table view data source if it wants to display any object type declared as supported by acceptedObjectClasses. So that's taken most of the hassle out of writing the table view data source — I've got just one, which can accept any combination of objects used anywhere in the app, yet it's very short and easy mentally to check for errors, and need never grow even as the app learns about more things that need to be displayed in tables.
Nobody ever explicitly imports those table view cells, because it'd just mean having to do the same work twice — declare the class in Objective-C, which the compiler will check for me, then go and redeclare it to the custom cut-down lookup system that I've implemented instead of just using Objective-C's, which I probably need to do manual verification on.

Answer 3

Click on a .m file in the Project Navigator on the left side of Xcode, then open the right-hand tile (with the right-hand "View" button in the toolbar) and look at the "Target Membership" section. There is a checkbox with your project name beside it. If the box is checked, that .m file is included in the build. If the checkbox is not checked then the .m is essentially ignored.
You can also check this by clicking on your project name at the top of the ProjectNavigator column, selecting the project under "TARGETS", selecting "Build Phases", and selecting "Compile Sources". All of the included .m files will be shown and you can add or delete files from the list using the + - buttons at the bottom of the list.