[swift-evolution] Pitch: Cross-module inlining and specialization

Slava Pestov spestov at apple.com
Mon Oct 2 22:23:26 CDT 2017

> On Oct 2, 2017, at 8:06 PM, Xiaodi Wu <xiaodi.wu at gmail.com> wrote:
> On Mon, Oct 2, 2017 at 9:55 PM, Slava Pestov <spestov at apple.com <mailto:spestov at apple.com>> wrote:
>> On Oct 2, 2017, at 7:52 PM, Kelvin Ma <kelvin13ma at gmail.com <mailto:kelvin13ma at gmail.com>> wrote:
>> Is this only a problem with fileprivate or does it extend to private members too? I feel like this would be a very valuable feature to support.
> Private members too. Consider this example,
> struct S {
>   private func f() {}
> }
> The member S.f mangles as _T06struct1SV1f33_AB643CAAAE0894CD0BC8584D7CA3AD23LLyyF. In this case, I suppose we won’t need the private discriminator because there can only be one S.f that’s directly a member of S, and not an extension. However imagine if two different source files both defined extensions of S, with a private member f. You would need to disambiguate them somehow.
> The simple-minded way to do this would be to require @_versioned annotations on private and fileprivate members to supply an internally unique alternative name to be used for mangling-as-though-internal (i.e. `@_versioned(my_extension_f)`). Such a function becoming public in an ABI-compatible way would require renaming the "actual" name to the unique @_versioned name.

We have _silgen_name for that, but we really don’t want to expose this more generally because people have been abusing it to make things visible to C, and they should be using @_cdecl instead.

> A more elegant refinement could be to have @_versioned private and fileprivate members mangled as though internal, erroring if two or more members with the same name are both @_versioned--would that work?

If you’re going to do that what is the value in having the capability at all?

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