All files are Objective-C++

Chrome back-end code is all C++ and we want to leverage many C++ features, such as stack-based classes and namespaces. As a result, all front-end Bling files should be .mm files, as we expect eventually they will contain C++ code or language features.

Use scoped_nsobject and WeakNSObject where ARC is not available.

While there are no smart pointers in Objective-C, Chrome has scoped_nsobject<T> and WeakNSObject<T> to automatically manage (and document) object ownership.

Under ARC,scoped_nsobject<T> and WeakNSObject<T> should only be used for interfacing with existing APIs that take these, or for declaring a C++ member variable in a header. Otherwise use __weak variables and strong/weak properties. Note that scoped_nsobject and WeakNSObject provide the same API under ARC, i.e. scoped_nsobject<T> foo([[Bar alloc] init]); is correct both under ARC and non-ARC.

scoped_nsobject<T> should be used for all owned member variables in C++ classes (except the private classes that only exist in implementation files) and Objective-C classes built without ARC, even if that means writing dedicated getters and setters to implement @property declarations. Same goes for WeakNSObject - always use it to express weak ownership of an Objective-C object, unless you are writing ARC code. We'd rather have a little more boilerplate code than a leak.

Use ObjCCast and ObjcCCastStrict

As the C++ style guide tells you, we never use C casts and prefer static_cast<T> and dynamic_cast<T>. However, for Objective-C casts we have two specific casts: base::mac::ObjCCast<T>arg is similar to dynamic_cast<T>, and ObjcCCastStrict DCHECKs against that class.


We follow Google style for blocks, except that historically we have used 2-space indentation for blocks that are parameters, rather than 4. You may continue to use this style when it is consistent with the surrounding code.


NOTREACHED: This function should not be called. If it is, we have a problem somewhere else. NOTIMPLEMENTED: This isn‘t implemented because we don’t use it yet. If it's called, then we need to figure out what it should do.

When something is called, but don't need an implementation, just comment that rather than using a logging macro.

TODO comments

Sometimes we include TODO comments in code. Generally we follow C++ style, but here are some more specific practices we've agreed upon as a team:

  • Every TODO must have a bug
  • Bug should be labeled with Hotlist-TODO-iOS
  • Always list bug in parentheses following “TODO”
    • // TODO( Something that needs doing.
    • Do NOT include http://
  • Optionally include a username for reference
  • Optionally include expiration date (make sure it's documented in the bug!)