[swift-evolution] [Proposal][Discussion] Modular Swift

Matthew Johnson matthew at anandabits.com
Tue Feb 21 22:11:36 CST 2017

> On Feb 21, 2017, at 9:47 PM, Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org> wrote:
>> On Feb 21, 2017, at 7:38 PM, Robert Widmann <devteam.codafi at gmail.com> wrote:
>> Correct.  Because, in dividing the submodule across an extension, you have placed what should be a private API into a differently-scoped location.
> Okay. So is your submodule design not intended to address the "I want to encapsulate implementation details so they're only visible to several units of code in different files, but not the entire module" use case? Because if there's no way to scope a symbol to "everything inside this submodule, but nothing outside this submodule", I think it leaves that use case unserved.

Unless I’m missing something there is also another encapsulation-related problem with the proposed design.  Let’s suppose for the sake of discussion there was a `submoduleprivate` access modifier (intentionally ungainly and not realistic).

// File 1
module Foo {
    // internal, visible to the whole module
    class Bar { submoduleprivate var protectedState: Int = 0 }

// File 2 - Has nothing to do with Foo at all
import MyModule.Foo

module NotFoo {
   // Hey, I need to see Bar.protectedState!!!
   func totallyNotFoo() {
       var bar = Bar()
       bar.foosExposedPrivates = 42

// ok, I’ll just add an extension to Foo so I can see submoduleprivate and wrap what I need
module Foo {
    // Hey, I’ll be nice and keep it fileprivate, but I could make it public if I wanted to.
    extension Bar {
         fileprivate var foosExposedPrivates: Int {
            // Yep, I’m inside Foo so I can see it’s submoduleprivate stuff
            get { return protectedState }
            set  { protectedState = newValue }

> -- 
> Brent Royal-Gordon
> Architechies
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