> On Jan 25, 2017, at 10:40 AM, Xiaodi Wu via swift-evolution 
> <swift-evolution@swift.org> wrote:
> This is contrary to several deliberate design decisions, if I understand 
> correctly.
> First, revisions to visibility rules in the Swift 3 timeline were made with 
> the deliberate intention that it should be possible to model greater 
> visibility within a type (e.g. public members) without actually exporting 
> that type. As Swift does not have optional warnings that can be turned off, 
> it would be incongruous if the language also warned users away from creating 
> internal types or variables before they are used. Unlike warnings about 
> unused variables within a scope, which are by definition local, a warning 
> such as proposed would be much more disruptive.
> Second, a variable with no access modifier defaults to internal, and this is 
> deliberate for the purpose of progressive disclosure (i.e. it is, by design, 
> possible for a new user to write useful code separated across multiple files 
> without learning what access modifiers are). This would be undone if nearly 
> every such use prompted a warning.
> In summary, I think the issue here is more one of style than safety, and IMO 
> is more within the scope of a linter.

One place a warning like this would be useful is with private/fileprivate code 
that resulted from migrating Swift 2 to 3. Xcode's automatic migrator naively 
changed all Swift 2 private declarations to fileprivate, since that's the 
obvious semantics-preserving change, but it's possible that this has had the 
knock-on effect that people overuse "fileprivate" because that's the example 
set by the migrator, and not for technical reasons. Given the number of ideas 
that have been raised about further extending or tweaking the visibility model 
since Swift 3, it's clear there's still some dissatisfaction with our current 
model, and we've been trying to get clear information about how well the 
existing model is working. Fileprivate is potentially overrepresented in code 
in the wild due to the migrator's behavior and people cargo-culting the 
migrator's code patterns, so a warning that suggested to users when they could 
make use of 'private' might help steer people to clean up their migrated code 
and give us a better idea of how well the model fits real-world problems.

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