[swift-evolution] [swift-evolution-announce] [Review] SE-0159: Fix Private Access Levels

[Drew Crawford]

On March 23, 2017 at 2:22:20 AM, David Hart (david at hartbit.com) wrote:

> We will get static linking at some point in the near future.
Static linking does not fix this issue. Just change "framework" to ".a".

> If we wait until we get submodules, we won't be able to revisit. This is probably our last chance to "remove" a feature. Submodules can always add features down the way.
Maybe submodules will solve this issue, maybe not.  But submodules are *much* more complex than scoped access:

* Performance.  This is hot code we compile with WMO.  Moving it into a submodule could reduce visibility for optimization in a way that causes a performance regression.  In particular, we know that specialization of T is a performance requirement, it isn't clear whether that would be preserved.  Does WMO provide the same visibility across submodules?  Nobody knows.

* Namespacing.  It's possible that one program may ship 3-4 versions of this code because each dependency has a slightly different version under our current samizdat process.  It is not clear whether submodules would avoid the "duplicate symbols" issue from C/ObjC.  Xiaodi seems quite concerned about a related "duplicate functions" problem involved with private today, doubling down on that is not a good idea.

* It is not clear whether submodules are from an objectcode point of view merged into the parent library or kept as individual libraries

* It is not clear from a .swiftmodule point of view whether submodules are merged into the parent module or distributed as .swiftmodules / .swiftdocs

* Not clear how much ABI impact there is from submodules at a time when we are supposed to be trying to stabilize it

I would love to believe that a proposal on submodules will come through having solutions to all these issues and many more, then we will implement it and all sing kumbayah.  But we are a long distance from that, and it may never happen at all, certainly we cannot evaluate proposals that haven't been written.  Meanwhile we have a solution in the hand.

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