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.
While there are no smart pointers in Objective-C, Chrome has
WeakNSObject<T> to automatically manage (and document) object ownership.
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
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.
As the C++ style guide tells you, we never use C casts and prefer
dynamic_cast<T>. However, for Objective-C casts we have two specific casts:
base::mac::ObjCCast<T>arg is similar to
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.
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:
// TODO(crbug.com/######): Something that needs doing.