On Mon, Jul 18, 2016 at 5:09 PM, Robert Widmann <[email protected]> wrote:
> > On Jul 18, 2016, at 3:00 PM, Xiaodi Wu <[email protected]> wrote: > > On Mon, Jul 18, 2016 at 4:49 PM, Robert Widmann <[email protected]> > wrote: > >> >> On Jul 18, 2016, at 2:32 PM, Xiaodi Wu <[email protected]> wrote: >> >> This is an interesting document. I think it deserves careful study. For >> now, some questions: >> >> What is the rationale behind permitting the using of specific methods? >> This seems to be usually fine-grained in comparison to other languages. >> What use cases do you have in mind for this? >> >> >> One use case: Swift libraries export not just member references as I’ve >> used here, but a large amount of free functions. It has long been a >> problem that free functions seem to pollute a shared namespace and there >> didn’t seem to be a clear way to hide them. >> > > Would a plausible simplification of the proposal be to have it > fine-grained enough to address free functions but not methods inside types? > Incidentally, although I do not see it in the proposal, I assume that * in > some form will be permitted (as in, `import Foundation using *`). > > >> I can see the use case for hiding specific symbols when they come into >> conflict with your own, but in your example you're hiding specific methods >> declared *in* an imported type. What is the use case here? Is it going to >> allow me to open backdoors so that, if I don't like `Foo.frobnicate()`, I >> can hide it and then substitute my own in an extension? This seems like a >> bad thing at first blush. >> >> >> For members that would be an acceptable use-case. The worst-case >> scenario that comes to mind is this being used as a way to “virtually >> override” a method in a subclass. Then again, the scope of the damage is >> limited to the file in which you’ve declared this monstrosity so clients >> and even you will not be able to see it outside of there unless you >> explicitly redeclare the hiding import (in which case, you probably know >> what you’re doing). >> >> A use care here might be hiding the KVO-ish parts of an object from >> yourself, or more generally subsetting out the part of an API you know you >> shouldn’t interact with in a particular submodule. >> >> >> I can see the obvious use case for renaming modules and types on >> import--basically, in my mind, it's like typealiases with hiding, and it's >> available in other languages of course. But how would renaming methods >> work? If Foo conforms to Equatable and I rename `Foo.==` to `Foo.!=`, is >> the type I import still Equatable? How would it behave? And even if Foo is >> fine, what happens if I try to subclass my Frankensteinian Foo? >> >> >> Of course you still conform to Equatable. The renaming defines a mapping >> from your names to “proper" names. For example, if you use a renaming >> import to change the requirements of a protocol in a file, then your >> conformance will simply look at the mapping and see that everything >> resolves into its proper place. Bear in mind that your renamings will not >> survive outside of the file in which you declare them. Frankenteinian Foo >> exists where you say it does and nowhere else. Everybody else just sees >> Foo conform to Equatable (unless they rename things themselves). >> > > Maybe let's work through an example: > > Suppose we have in stdlib: > > ``` > public protocol FooProtocol { > func frobnicate() > } > ``` > > Now, I write a library: > > ``` > import Swift.FooProtocol renaming (FooProtocol.frobnicate(), to: > FooProtocol.bobnicate()) > > public open class MyFoo : Swift.FooProtocol { > public open func bobnicate() { > print("Does your head hurt yet?") > } > } > ``` > > Now, you are an end user of my sinister library. > > What is the public API of `MyFoo`? > > > The proposal addresses this > > > Because import directives are file-local, they will never be exported > along with a `public` import and will > > default to exporting the entire contents of the module as though you had > never declared them. > > The user (and even you in other files that import this module) will see a > protocol conformance exactly as laid out in the Swift.FooProtocol module. > > For you, does `MyFoo` conform to `Swift.FooProtocol`? > > > It conforms because the renaming you wrote describes a way of resolving > FooProtocol.bobnicate() (your API) to FooProtocol.frobnicate() (everybody > else’s API). > > Can you call `MyFoo.frobnicate()`? How about `MyFoo.bobnicate()`? > > > What if you try to subclass `MyFoo`? > > > If you are inside the module you wrote the renaming, you will use it. If > you are outside of it, you will see the protocol requirement sans renaming. > > Does your subclass still conform to `Swift.FooProtocol`? > Do you override `bobnicate()` or `frobnicate()`? > My head hurts… > > > Because you have explicitly renamed the protocol requirement, you will > override the same protocol requirement both inside and outside this module > but your renaming will not propagate to other files unless they themselves > opt in the way you have here. It would be particularly sinister if you > could arbitrarily edit the user-facing API of members simply by importing a > library. > Sounds good. If I understand you correctly, by conforming `MyFoo` to an internally renamed `Swift.FooProtocol`, the renaming of the user-facing API for `FooProtocol` means that the public API of `MyFoo` is changed so that, outside the module, it has a member `frobnicate()` and no longer has a member `bobnicate()`? > > >> >> >> On Mon, Jul 18, 2016 at 16:10 Robert Widmann via swift-evolution < >> [email protected]> wrote: >> >>> Hello all, >>> >>> TJ Usiyan, Harlan Haskins, and I have been working on a proposal to >>> rework qualified imports and introduce an explicit module system to Swift >>> that we’d like to publish for your viewing pleasure. >>> >>> The initial impetus was set out in a radar (rdar://17630570) I sent >>> fairly early on that didn’t receive a response, so I started a >>> swift-evolution >>> <http://permalink.gmane.org/gmane.comp.lang.swift.evolution/1378> thread >>> discussing the basics of this proposal. It has been refined and expanded a >>> bit to include an effort to make Swift modules explicit and updated with >>> the feedback of that first thread. Contents of the proposal are inline and >>> can >>> also be had as a gist >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6> or on >>> Github. <https://github.com/apple/swift-evolution/pull/440> >>> >>> Cheers, >>> >>> ~Robert Widmann >>> >>> Qualified Imports and Modules >>> >>> - Proposal: SE-NNNN >>> <https://gist.github.com/CodaFi/NNNN-first-class-qualified-imports.md> >>> - Authors: Robert Widmann <https://github.com/codafi>, Harlan Haskins >>> <https://github.com/harlanhaskins>, TJ Usiyan >>> <https://github.com/griotspeak> >>> - Status: Awaiting review >>> - Review manager: TBD >>> >>> >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#introduction> >>> Introduction >>> >>> We propose a complete overhaul of the qualified imports syntax and >>> semantics and the introduction of a module system. >>> >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#motivation> >>> Motivation >>> >>> Swift code is modular by default. However, it is not clear how to >>> decompose existing modules further into submodules. In addition, it is >>> difficult to tell how importing a module affects its export to consumers of >>> a library. This leads many to either fake namespaces with enums, attempt to >>> structure Swift code with modulemaps, or use a large amount of >>> version-control submodules. All of these can be rolled into one complete >>> package in the form of a comprehensive rethink of the qualified import >>> system and the introduction of a module system. >>> >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#proposed-solution>Proposed >>> solution >>> >>> Modules will now become an explicit part of working with canonical Swift >>> code. The grammar and semantics of qualified imports will change completely >>> with the addition of *import qualifiers* and *import directives*. We >>> also introduce three new contextual keywords: using, hiding, and >>> renaming, to facilitate fine-grained usage of module contents. >>> >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#detailed-design>Detailed >>> design >>> >>> Qualified import syntax will be revised to the following >>> >>> module-decl -> module <module-path> >>> import-decl -> <access-level-modifier> import <module-path> <(opt) >>> import-directive-list> >>> module-path -> <identifier> >>> -> <identifier>.<import-path> >>> import-directive-list -> <import-directive> >>> -> <import-directive> <import-directive-list> >>> import-directive -> using (<identifier>, ...) >>> -> hiding (<identifier>, ...) >>> -> renaming (<identifier>, to: <identifier>, ...) >>> >>> This introduces the concept of an import *directive*. An import >>> directive is a file-local modification of an imported identifier. A >>> directive can be one of 3 operations: >>> >>> 1) *using*: The *using* directive is followed by a list of identifiers >>> within the imported module that should be exposed to this file. >>> >>> // The only visible parts of Foundation in this file are // Date.init(), >>> Date.hashValue, and Date.description.import Foundation.Date using >>> (Date.init(), Date.hashValue, Date.description) >>> >>> 2) *hiding*: The hiding directive is followed by a list of identifiers >>> within the imported module that should be hidden from this file. >>> >>> // Imports all of Foundation.Date except `Date.compare()`import >>> Foundation.Date hiding (Date.compare()) >>> >>> 3) *renaming*: The renaming directive is followed by a list of >>> identifiers separated by to: that should be exposed to this file but >>> renamed. >>> >>> // Imports all of Dispatch.DispatchQueue but renames the static member // >>> DispatchQueue.main, to DispatchQueue.mainQueueimport Dispatch.DispatchQueue >>> renaming (DispatchQueue.Type.main to: DispatchQueue.Type.mainQueue)// >>> Renaming can also rename modules. All members of UIKit have to be >>> qualified with// `UI` now.import UIKit renaming (UIKit, to: UI) >>> >>> Import directives chain to one another and can be used to create a >>> fine-grained module import: >>> >>> // Imports all of Foundation except `DateFormatter` and renames `Cache` to >>> `LRUCache`import Foundation hiding (DateFormatter) renaming (Cache to: >>> LRUCache)// Imports SCNNode except SCNNode.init(mdlObject:) and renames >>> `.description` to// `.nodeDescription` import SceneKit using (SCNNode) >>> renaming (SCNNode.description, to: SCNNode.nodeDescription) >>> hiding (SCNNode.init(mdlObject:)) >>> >>> Directive chaining occurs left-to-right: >>> >>> // This says to 1) Hide nothing 2) Use nothing 3) rename Int to INT. It is >>> invalid// because 1) We will show everything 2) Then hide everything 3) >>> Therefore Int is unavailable, error.import Swift hiding () using () >>> renaming (Int, to: INT)// This says to 1) Use Int 2) Hide String 3) rename >>> Double to Triple. It is invalid// because 1) Int is available 2) String is >>> not, error. 3) Double is unavailable, error.import Swift using (Int) hiding >>> (String) renaming (Double, to: Triple)// Valid. This will be merged as >>> `using (Int)`import Swift using () using (Int)// Valid. This will be >>> merged as `hiding (String, Double)`import Swift hiding (String) hiding >>> (Double) hiding ()// Valid (if redundant). This will be merged as `using >>> ()`import Swift using (String) hiding (String) >>> >>> Module scope is delimited by the keyword module followed by a fully >>> qualified name and must occur as the first declaration in a file. For >>> example: >>> >>> // ./Math/Integers/Arithmetic.swift >>> module Math.Integers.Arithmetic >>> public protocol _IntegerArithmetic {} >>> public struct _Abs {} >>> @_versionedinternal func _abs<Args>(_ args: Args) -> (_Abs, Args) {} >>> // ./Math/Integers.swift >>> module Math.Integers >>> // _abs is visible in this module and all others within the project, // but >>> is not exported along with it.internal import Math.Integers.Arithmetic >>> public protocol IntegerArithmetic : _IntegerArithmetic, Comparable {}public >>> protocol SignedNumber : Comparable, ExpressibleByIntegerLiteral {} >>> >>> // Math.swift >>> module Math >>> // Exports the entire public contents of Math.Integers, but nothing in // >>> Math.Integers.Arithmetic.public import Math.Integers >>> >>> Modules names are tied to a directory structure that describes their >>> location relative to the current module and it will now be an error to >>> violate this rule. For example: >>> >>> module String // lives in ./String.swift >>> module String.Core // lives in ./String/Core.swift >>> module String.Core.Internals.Do.You.Even.Write // lives in >>> ./String/Core/Internals/Do/You/Even/Write.swift >>> >>> Existing projects that do not adopt these rules will still retain their >>> *implicit >>> module name* (usually defined as the name of the framework or >>> application that is being built) and may continue to use whatever directory >>> structure they wish, however they may not declare any explicit modules. >>> >>> This proposal also solves the problem of module *export*. A module that >>> is imported without an access level modifier will default to an internal >>> import >>> per usual. However, when it is useful to fully expose the public content of >>> submodules to a client, a public modifier can be used. Similarly, when >>> it is useful to access internal or [file]private APIs, but not expose >>> them to clients, those access modifiers may be used. The rule of thumb is: >>> Only identifiers that are at least as visible as the qualifier on the >>> import make for valid import declarations. For example: >>> >>> // A submodule declaring a `private` class that gets imported with // an >>> `internal` qualifier with a `using` directive is an invalid import // >>> declaration. >>> module Foo.Bar >>> private class PrivateThing {} >>> >>> module Foo >>> // Error: PrivateThing not visible, use `private import`import Foo.Bar >>> using (PrivateThing) >>> >>> // However, a submodule declaring a `public` struct that gets imported with >>> // an `private` qualifier is a valid import declaration. >>> module Foo.Bar >>> public class PublicThing {} >>> >>> module Foo >>> // All good! Foo can see Foo.Bar.PrivateThing.private import Foo.Bar using >>> (PublicThing) >>> >>> Because import directives are file-local, they will never be exported >>> along with a public import and will default to exporting the entire >>> contents of the module as though you had never declared them. >>> >>> // In this file and this file alone, the directives apply. To the user// >>> of this module, it is as though this declaration were simply:// public >>> import Foundation.Datepublic import Foundation.Date hiding (Date.init()) >>> renaming (Date.Type.distantPast, >>> to: Date.Type.letsGoLivingInThePast, >>> >>> Date.Type.timeIntervalSinceReferenceDate, >>> to: Date.Type.startOfTheUniverse) >>> renaming (Date.Type.<, to: Date.Type.<<<<<) >>> >>> >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#impact-on-existing-code>Impact >>> on existing code >>> >>> Existing code that is using qualified module import syntax (import >>> {func|class|typealias|class|struct|enum|protocol} <qualified-name>) >>> will be deprecated. Code that is not organized into modules will remain >>> unaffected and organized into one contiguous top-level module. However, it >>> is strongly recommended that frameworks be decomposed and reorganized >>> around the new module system. >>> >>> As a case study, the public interface to the standard library appears to >>> already be mostly broken down into submodules as described in >>> GroupInfo.json >>> <https://github.com/apple/swift/blob/master/stdlib/public/core/GroupInfo.json> >>> . >>> >>> Code that is defined in modulemaps already defines a module structure >>> that can be imported directly into this scheme. >>> >>> <https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#alternatives-considered>Alternatives >>> considered >>> >>> Module export can also be placed on the module declaration itself. The >>> relevant parts of the grammar that have changed are below with an example: >>> >>> module-decl -> <access-level-modifier> module <module-path> >>> import-decl -> import <module-path> <(opt) import-directive-list> >>> >>> private module String.Core.Internals >>> // Shh, it's a secret. >>> >>> While this style makes it immediately obvious to the library author >>> which modules are public or private, it causes the consumer problems >>> because submodule exports are no longer explicit and are entirely ad-hoc. >>> In the interest of enabling, for one, users of IDEs to drill into public >>> submodules, making export local to import seems more appropriate. >>> _______________________________________________ >>> swift-evolution mailing list >>> [email protected] >>> https://lists.swift.org/mailman/listinfo/swift-evolution >> >> >
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