Hello everybody. Please excuse this proposal’s poor formatting. I am very new
to swift-evolution and don’t yet know how to do a formatted proposal. :)
Proposal
I am proposing to add an implement keyword to go with protocol method
implementations like the override keyword.
Motivation
When writing an implementation for a protocol method, there is no indication
that the method is an implementation of a protocol method. Unless it is a
well-known protocol like UITableViewDataSource, there is simply no way to know
if the method is provided by a protocol or the enclosing class. Right now, the
only way to guess if a method is protocol-provided is if it follows the pattern
of someObjectOrView(_: requestSomething:) or someObjectOrView(_:
somethingDidHappen:). But since non-Cocoa protocol methods may not follow that
pattern, they will not be so easy to guess. Here’s an example illustrating the
problem:
func recordInDatabase(database: TJDatabase, atIndexPath indexPath: NSIndexPath)
-> TJRecord {
//…
}
Is this a protocol method implementation, or simply a method declaration? Well,
it looks like a protocol method implementation, but how can one be sure? There
is no way to definitely know unless you are familiar with it or you found its
declaration after searching in the whole project, worse in huge projects. The
method above just seems too “ordinary” to be a protocol method implementation.
Even worse, some developer might come around and even rename that method, and
there would be an error, then he has to fish around for the protocol method
he’s missing. Assuming that he finally found it (if the protocol is small
enough), he might even implement it again with the same code as the renamed
method. We can see the problem here.
Or, let’s think about this: how would it feel if there is no override keyword?
How would one know if a method is an override or not? We can see how this
relates to the confusion with protocol method implementations.
Proposed solution
The proposed solution is to add an implement keyword, which improves the code
above to this:
implement func recordInDatabase(database: TJDatabase, atIndexPath indexPath:
NSIndexPath) -> TJRecord {
//…
}
Now it is very clear that we are implementing a protocol method rather than
declaring a method. The code is much clearer, and it doesn’t hurt the
readability either.
Detailed design
When overriding implemented protocol methods from a superclass, the override
keyword is still used:
override func recordInDatabase(database: TJDatabase, atIndexPath indexPath:
NSIndexPath) -> TJRecord {
return super.recordInDatabase(database, atIndexPath: indexPath)
}
Impact on existing code
Existing code would be changed to include the implement keyword in appropriate
places. This could be handled via the Swift latest syntax converter in Xcode.
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