|
|
|
|
|
<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="API documentation for the Rust `StableDeref` trait in crate `stable_deref_trait`."><meta name="keywords" content="rust, rustlang, rust-lang, StableDeref"><title>stable_deref_trait::StableDeref - Rust</title><link rel="stylesheet" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc trait"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../stable_deref_trait/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Trait StableDeref</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#foreign-impls">Implementations on Foreign Types</a><div class="sidebar-links"><a href="#impl-StableDeref-for-%26%27a%20T">&'a T</a><a href="#impl-StableDeref-for-%26%27a%20mut%20T">&'a mut T</a><a href="#impl-StableDeref-for-Arc%3CT%3E">Arc<T></a><a href="#impl-StableDeref-for-Box%3CT%3E">Box<T></a><a href="#impl-StableDeref-for-MutexGuard%3C%27a%2C%20T%3E">MutexGuard<'a, T></a><a href="#impl-StableDeref-for-Rc%3CT%3E">Rc<T></a><a href="#impl-StableDeref-for-Ref%3C%27a%2C%20T%3E">Ref<'a, T></a><a href="#impl-StableDeref-for-RefMut%3C%27a%2C%20T%3E">RefMut<'a, T></a><a href="#impl-StableDeref-for-RwLockReadGuard%3C%27a%2C%20T%3E">RwLockReadGuard<'a, T></a><a href="#impl-StableDeref-for-RwLockWriteGuard%3C%27a%2C%20T%3E">RwLockWriteGuard<'a, T></a><a href="#impl-StableDeref-for-String">String</a><a href="#impl-StableDeref-for-Vec%3CT%3E">Vec<T></a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='index.html'>stable_deref_trait</a></p><script>window.sidebarCurrent = {name: 'StableDeref', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../settings.html"><img src="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#124' title='goto source code'>[src]</a></span><span class='in-band'>Trait <a href='index.html'>stable_deref_trait</a>::<wbr><a class="trait" href=''>StableDeref</a></span></h1><div class="docblock type-decl hidden-by-usual-hider"><pre class='rust trait'>pub unsafe trait StableDeref: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/deref/trait.Deref.html" title="trait core::ops::deref::Deref">Deref</a> { }</pre></div><div class='docblock'><p>An unsafe mark
|
|
|
|
|
|
<p>More specifically, implementors must ensure that the result of calling deref() is valid for the lifetime of the object, not just the lifetime of the borrow, and that the deref is valid even if the object is moved. Also, it must be valid even after invoking arbitrary &self methods or doing anything transitively accessible from &Self. If Self also implements DerefMut, the same restrictions apply to deref_mut() and it must remain valid if anything transitively accessible from the result of deref_mut() is mutated/called. Additionally, multiple calls to deref, (and deref_mut if implemented) must return the same address. No requirements are placed on &mut self methods other than deref_mut() and drop(), if applicable.</p>
|
|
|
|
|
|
<p>Basically, it must be valid to convert the result of deref() to a pointer, and later dereference that pointer, as long as the original object is still live, even if it has been moved or &self methods have been called on it. If DerefMut is also implemented, it must be valid to get pointers from deref() and deref_mut() and dereference them while the object is live, as long as you don't simultaneously dereference both of them.</p>
|
|
|
|
|
|
<p>Additionally, Deref and DerefMut implementations must not panic, but users of the trait are not allowed to rely on this fact (so that this restriction can be removed later without breaking backwards compatibility, should the need arise).</p>
|
|
|
|
|
|
<p>Here are some examples to help illustrate the requirements for implementing this trait:</p>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
|
|
|
|
|
<span class="kw">struct</span> <span class="ident">Foo</span>(<span class="ident">u8</span>);
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">u8</span>;
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">Target</span> { <span class="kw-2">&</span><span class="self">self</span>.<span class="number">0</span> }
|
|
|
|
|
|
}</pre></div>
|
|
|
|
|
|
<p>Foo cannot implement StableDeref because the int will move when Foo is moved, invalidating the result of deref().</p>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
|
|
|
|
|
<span class="kw">struct</span> <span class="ident">Foo</span>(<span class="ident">Box</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>);
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">u8</span>;
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">Target</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="number">0</span> }
|
|
|
|
|
|
}</pre></div>
|
|
|
|
|
|
<p>Foo can safely implement StableDeref, due to the use of Box.</p>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
|
|
|
|
|
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>)]</span>
|
|
|
|
|
|
<span class="kw">struct</span> <span class="ident">Foo</span>(<span class="ident">Rc</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>);
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">u8</span>;
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">Target</span> { <span class="kw-2">&</span><span class="kw-2">*</span><span class="self">self</span>.<span class="number">0</span> }
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">Self</span>::<span class="ident">Target</span> { <span class="ident">Rc</span>::<span class="ident">make_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="number">0</span>) }
|
|
|
|
|
|
}</pre></div>
|
|
|
|
|
|
<p>This is a simple implementation of copy-on-write: Foo's deref_mut will copy the underlying int if it is not uniquely owned, ensuring unique access at the point where deref_mut() returns. However, Foo cannot implement StableDeref because calling deref_mut(), followed by clone().deref() will result in mutable and immutable references to the same location. Note that if the DerefMut implementation were removed, Foo could safely implement StableDeref. Likewise, if the Clone implementation were removed, it would be safe to implement StableDeref, although Foo would not be very useful in that case, (without clones, the rc will always be uniquely owned).</p>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
|
|
|
|
|
<span class="kw">struct</span> <span class="ident">Foo</span>;
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">str</span>;
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">Target</span> { <span class="kw-2">&</span><span class="string">"Hello"</span> }
|
|
|
|
|
|
}</pre></div>
|
|
|
|
|
|
<p>Foo can safely implement StableDeref. It doesn't own the data being derefed, but the data is gaurenteed to live long enough, due to it being 'static.</p>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
|
|
|
|
|
<span class="kw">struct</span> <span class="ident">Foo</span>(<span class="ident">Cell</span><span class="op"><</span><span class="ident">bool</span><span class="op">></span>);
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">str</span>;
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">Target</span> {
|
|
|
|
|
|
<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="self">self</span>.<span class="number">0</span>.<span class="ident">get</span>();
|
|
|
|
|
|
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">set</span>(<span class="op">!</span><span class="ident">b</span>);
|
|
|
|
|
|
<span class="kw">if</span> <span class="ident">b</span> { <span class="kw-2">&</span><span class="string">"Hello"</span> } <span class="kw">else</span> { <span class="kw-2">&</span><span class="string">"World"</span> }
|
|
|
|
|
|
}
|
|
|
|
|
|
}</pre></div>
|
|
|
|
|
|
<p>Foo cannot safely implement StableDeref, even though every possible result of deref lives long enough. In order to safely implement StableAddress, multiple calls to deref must return the same result.</p>
|
|
|
|
|
|
|
|
|
|
|
|
<div class="example-wrap"><pre class="rust rust-example-rendered">
|
|
|
|
|
|
<span class="kw">struct</span> <span class="ident">Foo</span>(<span class="ident">Box</span><span class="op"><</span>(<span class="ident">u8</span>, <span class="ident">u8</span>)<span class="op">></span>);
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">Deref</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">type</span> <span class="ident">Target</span> <span class="op">=</span> <span class="ident">u8</span>;
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="self">Self</span>::<span class="ident">Target</span> { <span class="kw-2">&</span><span class="self">self</span>.<span class="number">0</span>.<span class="ident">deref</span>().<span class="number">0</span> }
|
|
|
|
|
|
}
|
|
|
|
|
|
<span class="kw">impl</span> <span class="ident">DerefMut</span> <span class="kw">for</span> <span class="ident">Foo</span> {
|
|
|
|
|
|
<span class="kw">fn</span> <span class="ident">deref_mut</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">Self</span>::<span class="ident">Target</span> { <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>.<span class="number">0</span>.<span class="ident">deref_mut</span>().<span class="number">1</span> }
|
|
|
|
|
|
}</pre></div>
|
|
|
|
|
|
<p>Foo cannot implement StableDeref because deref and deref_mut return different addresses.</p>
|
|
|
|
|
|
</div>
|
|
|
|
|
|
<h2 id='foreign-impls' class='small-section-header'>Implementations on Foreign Types<a href='#foreign-impls' class='anchor'></a></h2><h3 id='impl-StableDeref-for-Box%3CT%3E' class='impl'><code class='in-band'>impl<T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> <a class="trait" href="../stable_deref_trait/trait.StableDeref.html" title="trait stable_deref_trait::StableDeref">StableDeref</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/boxed/struct.Box.html" title="struct alloc::boxed::Box">Box</a><T></code><a href='#impl-StableDeref-for-Box%3CT%3E' class='anchor'></a><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#173' title='goto source code'>[src]</a></h3><div class='impl-items'></div><h3 id='impl-StableDeref-for-Vec%3CT%3E' class='impl'><code class='in-band'>impl<T> <a class="trait" href="../stable_deref_trait/trait.StableDeref.html" title="trait stable_deref_trait::StableDeref">StableDeref</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a><T></code><a href='#impl-StableDeref-for-Vec%3CT%3E' class='anchor'></a><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#175' title='goto source code'>[src]</a></h3><div class='impl-items'></div><h3 id='impl-StableDeref-for-String' class='impl'><code class='in-band'>impl <a class="trait" href="../stable_deref_trait/trait.StableDeref.html" title="trait stable_deref_trait::StableDeref">StableDeref</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/string/struct.String.html" title="struct alloc::string::String">String</a></code><a href='#impl-StableDeref-for-String' class='anchor'></a><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#177' title='goto source code'>[src]</a></h3><div class='impl-items'></div><h3 id='impl-StableDeref-for-Rc%3CT%3E' class='impl'><code class='in-band'>impl<T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> <a class="trait" href="../stable_deref_trait/trait.StableDeref.html" title="trait stable_deref_trait::StableDeref">StableDeref</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/rc/struct.Rc.html" title="struct alloc::rc::Rc">Rc</a><T></code><a href='#impl-StableDeref-for-Rc%3CT%3E' class='anchor'></a><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#180' title='goto source code'>[src]</a></h3><div class='impl-items'></div><h3 id='impl-StableDeref-for-Arc%3CT%3E' class='impl'><code class='in-band'>impl<T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> <a class="trait" href="../stable_deref_trait/trait.StableDeref.html" title="trait stable_deref_trait::StableDeref">StableDeref</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/alloc/sync/struct.Arc.html" title="struct alloc::sync::Arc">Arc</a><T></code><a href='#impl-StableDeref-for-Arc%3CT%3E' class='anchor'></a><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#184' title='goto source code'>[src]</a></h3><div class='impl-items'></div><h3 id='impl-StableDeref-for-Ref%3C%27a%2C%20T%3E' class='impl'><code class='in-band'>impl<'a, T: ?<a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> <a class="trait" href="../stable_deref_trait/trait.StableDeref.html" title="trait stable_deref_trait::StableDeref">StableDeref</a> for <a class="struct" href="https://doc.rust-lang.org/nightly/core/cell/struct.Ref.html" title="struct core::cell::Ref">Ref</a><'a, T></code><a href='#impl-StableDeref-for-Ref%3C%27a%2C%20T%3E' class='anchor'></a><a class='srclink' href='../src/stable_deref_trait/lib.rs.html#189' title='goto source code'>[src]</a></h3><div class='impl-items'></div><h3
|
|
|
|
|
|
<h2 id='implementors' class='small-section-header'>Implementors<a href='#implementors' class='anchor'></a></h2><div class='item-list' id='implementors-list'></div><span class='loading-content'>Loading content...</span><script type="text/javascript">window.inlined_types=new Set([]);</script><script type="text/javascript" async
|
|
|
|
|
|
src="../implementors/stable_deref_trait/trait.StableDeref.js">
|
|
|
|
|
|
</script></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g., <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g., <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g., <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../";window.currentCrate = "stable_deref_trait";</script><script src="../aliases.js"></script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html>
|
