[swift-evolution] Proposal: Re-instate mandatory self for accessing instance properties and functions

Honza Dvorsky czechboy0 at gmail.com
Tue Dec 15 16:46:19 CST 2015

Hi all,

I've been following the thread from the beginning and some great arguments
have been layed out. As far as I understand, this proposal would lead to
fewer correctness bugs (referring to a different variable due to implicit
self, has happened to me twice in the last couple of months, was very hard
to track down).

The disadvantages of this are only verbosity. But, from the design
principles of Swift (as I understand them), correctness is preferred over
making the language concise, especially when those two are in conflict,
just like here.

I support the proposal, because it would lead to fewer bugs at only the
cost of extra few characters. Again, I've been bitten by implicit self a
couple times before and those bugs are hard to track down. And the
readability of the code in code reviews, to me, is another huge advantage,
possibly leading to more correctness bugs caught early.

I understand and appreciate the disadvantages, but again, I believe we
should prefer correctness over conciseness, as explicitly stated by the
Swift design principles.
On Tue, Dec 15, 2015 at 11:28 PM Slava Pestov via swift-evolution <
swift-evolution at swift.org> wrote:

> Hi all,
> I don't see anyone lay out how this proposal can interact with nested
> types and such. There's a fair amount of complexity in Swift with what you
> can do by nesting things inside of each other, so the simple conceptual
> model of "locals are unqualified, instance variables have a self. prefix"
> doesn't seem to generalize.
> Will I need to qualify associated types with the protocol or type name to
> refer to them? What about generic type parameters, they're sort of like
> "instance variables" too.
> What about class methods that want to call each other? Do they need the
> explicit 'self', or an explicit class name prefix? The latter changes
> semantics if the class method is overridden in a subclass.
> If we ever add the ability for an inner type to capture stored properties
> from the outer type, how do you reference properties of the outer type? I
> guess the problem has to be solved anyway to refer to an outer "self"
> explicitly, but qualifying everything with OuterType.self.foo kind of
> defeats the purpose of inner types altogether.
> I'm not sure I buy the readability arguments in favor of this approach. It
> seems the languages where explicit 'self' was adopted did it mostly by
> accident, or because of implementation concerns. In Python for instance,
> there's no way for assignment to modify a binding in an outer scope, so
> 'foo = bar' always sets a local named 'foo', IIRC. So explicit self is
> needed there. Greg Parker explains earlier in this thread by explicit self
> was chosen for Objective-C, and it wasn't readability.
> Slava
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