<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><span></span></div><div><div>There was an exchange in the past on how extensions are very different from swift nominal/structural types, and Doug even shared how adding scoping to extensions is not a trivial task by a long shot. In this context, talking about unifying modifier behaviors does not make much sense to me. I am not sure i understand what motivates this change.</div><div id="AppleMailSignature"><div>Regards</div>(From<span class="Apple-style-span" style="-webkit-tap-highlight-color: rgba(26, 26, 26, 0.294118);"> mobile)</span></div><div><br>On Jun 26, 2016, at 8:59 PM, Adrian Zubarev via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><style>
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.error { color:#AA0000; }</style><div class="bloop_markdown"><p>Proposal is moved to a git repo: <a href="https://github.com/DevAndArtist/swift-evolution/blob/extensions_access_modifiers/proposals/nnnn-extensions-access-modifiers.md">https://github.com/DevAndArtist/swift-evolution/blob/extensions_access_modifiers/proposals/nnnn-extensions-access-modifiers.md</a></p>
<ul>
<li>I also updated a few things for readability.</li>
</ul>
<hr>
<h1 id="revisingaccessmodifiersonextensions">Revising access modifiers on extensions</h1>
<ul>
<li>Proposal: <a href="nnnn-extensions-access-modifiers.md">SE-NNNN</a></li>
<li>Author: <a href="https://github.com/DevAndArtist">Adrian Zubarev</a></li>
<li>Status: <strong><a href="#rationale">Awaiting review</a></strong></li>
<li>Review manager: TBD</li>
</ul>
<h2 id="introduction">Introduction</h2>
<p>One great goal for Swift 3 is to sort out any source breaking language changes. This proposal aims to fix access modifier inconsistency on extensions compared to other scope declarations types.</p>
<p>Swift-evolution thread: <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160620/022144.html">[Proposal] Revising access modifiers on extensions</a></p>
<h2 id="motivation">Motivation</h2>
<p>When declaring members on extensions which don’t have an explicit access modifier in Swift 2.2, it is possible to create an <strong>implicitly public extension</strong> by applying a <em>public</em> modifier to at least one extension member.</p>
<pre><code class="swift">public struct A { … }
// Implicitly public
extension A {
public var member1: SomeType { … }
// Implicitly internal
func member2() { … }
}
// Implicitly internal
extension A {
// Implicitly internal
var member3: SomeType { … }
}
</code></pre>
<p>Furthermore in Swift 2.2 it is not allowed to apply an <em>access modifier</em> on extensions when a <em>type inheritance clause</em> is present:</p>
<pre><code class="swift">public protocol B { … }
// 'public' modifier cannot be used with
// extensions that declare protocol conformances
public extension A : B { … }
</code></pre>
<h2 id="proposedsolution">Proposed solution</h2>
<ol>
<li><p>Allow access modifier on extensions when a type inheritance clause is present.</p></li>
<li><p>Remove the behavior of an implicit public extension.</p></li>
</ol>
<p>This changes should make access modifier on extensions consistent to classes, structs and enums (and <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0025-scoped-access-level.md">SE–0025</a>).</p>
<h4 id="thecurrentgrammarwillnotchange:">The current grammar will not change:</h4>
<p><em>extension-declaration</em> → <em>access-level-modifier</em><sub>opt</sub> <strong>extension</strong> <em>type-identifier</em> <em>type-inheritance-clause</em><sub>opt</sub> <em>extension-body</em></p>
<p><em>extension-declaration</em> → <em>access-level-modifier</em><sub>opt</sub> <strong>extension</strong> <em>type-identifier</em> <em>requirement-clause</em> <em>extension-body</em></p>
<p><em>extension-body</em> → <strong>{</strong> <em>declarations</em><sub>opt</sub> <strong>}</strong></p>
<p>Iff the <em>access-level-modifier</em> is not present, the access modifier on extensions should always be implicitly <strong>internal</strong>.</p>
<h4 id="impactonapis:">Impact on APIs:</h4>
<p>Current version:</p>
<pre><code class="swift">/// Implementation version
///========================
public protocol Y {
func member()
}
public struct X { … }
// Implicitly public
extension X : Y {
public func member() { ... }
// Implicitly internal
func anotherMember() { ... }
}
/// Imported modele version
///========================
public protocol Y {
func member()
}
public struct X { ... }
// Missing `public` modifier
extension X : Y {
public func member() { ... }
}
</code></pre>
<p>New Version:</p>
<pre><code class="swift">/// Implementation version
///========================
public extension X : Y {
public func member() { ... }
// Implicitly internal
func anotherMember() { ... }
}
/// Imported modele version
///========================
public extension X : Y {
public func member() { ... }
}
</code></pre>
<h2 id="impactonexistingcode">Impact on existing code</h2>
<p>This is a source-breaking change that can be automated by a migrator, by simply scanning the <em>extension-body</em> for at least one <em>public</em> modifier on its members. Iff a <em>public</em> modifier was found on any member, the migrator can add an explicit <em>public</em> modifier to the extension itself.</p>
<h2 id="alternativesconsidered">Alternatives considered</h2>
<ul>
<li>No other alternative were considered for this proposal.</li>
</ul>
<h2 id="rationale">Rationale</h2>
<p>On [Date], the core team decided to <strong>(TBD)</strong> this proposal.
When the core team makes a decision regarding this proposal,
their rationale for the decision will be written here.</p>
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