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<p class='location'>Trait Fail</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#provided-methods">Provided Methods</a><div class="sidebar-links"><a href="#method.cause">cause</a><a href="#method.backtrace">backtrace</a><a href="#method.context">context</a><a href="#method.compat">compat</a><a href="#method.causes">causes</a><a href="#method.root_cause">root_cause</a></div><a class="sidebar-title" href="#implementors">Implementors</a><a class="sidebar-title" href="#methods">Methods</a><div class="sidebar-links"><a href="#method.downcast_ref">downcast_ref</a><a href="#method.downcast_mut">downcast_mut</a><a href="#method.root_cause">root_cause</a><a href="#method.causes">causes</a></div></div><p class='location'><a href='index.html'>failure</a></p><script>window.sidebarCurrent = {name: 'Fail', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Trait <a href='index.html'>failure</a>::<wbr><a class="trait" href=''>Fail</a></span><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>]
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</span><a class='srclink' href='../src/failure/lib.rs.html#86-162' title='goto source code'>[src]</a></span></h1>
<pre class='rust trait'>pub trait Fail: <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html" title="trait core::fmt::Display">Display</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html" title="trait core::fmt::Debug">Debug</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + 'static {
fn <a href='#method.cause' class='fnname'>cause</a>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><&<a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a>> { ... }
<div class='item-spacer'></div> fn <a href='#method.backtrace' class='fnname'>backtrace</a>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><&<a class="struct" href="../failure/struct.Backtrace.html" title="struct failure::Backtrace">Backtrace</a>> { ... }
<div class='item-spacer'></div> fn <a href='#method.context' class='fnname'>context</a><D>(self, context: D) -> <a class="struct" href="../failure/struct.Context.html" title="struct failure::Context">Context</a><D><br> <span class="where">where<br> D: <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html" title="trait core::fmt::Display">Display</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + 'static,<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>,
{ ... }
<div class='item-spacer'></div> fn <a href='#method.compat' class='fnname'>compat</a>(self) -> <a class="struct" href="../failure/struct.Compat.html" title="struct failure::Compat">Compat</a><Self><br> <span class="where">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>,
{ ... }
<div class='item-spacer'></div> fn <a href='#method.causes' class='fnname'>causes</a>(&self) -> <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><br> <span class="where">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>,
{ ... }
<div class='item-spacer'></div> fn <a href='#method.root_cause' class='fnname'>root_cause</a>(&self) -> &<a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a><br> <span class="where">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>,
{ ... }
}</pre><div class='docblock'><p>The <code>Fail</code> trait.</p>
<p>Implementors of this trait are called 'failures'.</p>
<p>All error types should implement <code>Fail</code>, which provides a baseline of
functionality that they all share.</p>
<p><code>Fail</code> has no required methods, but it does require that your type
implement several other traits:</p>
<ul>
<li><code>Display</code>: to print a user-friendly representation of the error.</li>
<li><code>Debug</code>: to print a verbose, developer-focused representation of the
error.</li>
<li><code>Send + Sync</code>: Your error type is required to be safe to transfer to and
reference from another thread</li>
</ul>
<p>Additionally, all failures must be <code>'static</code>. This enables downcasting.</p>
<p><code>Fail</code> provides several methods with default implementations. Two of these
may be appropriate to override depending on the definition of your
particular failure: the <code>cause</code> and <code>backtrace</code> methods.</p>
<p>The <code>failure_derive</code> crate provides a way to derive the <code>Fail</code> trait for
your type. Additionally, all types that already implement
<code>std::error::Error</code>, and are also <code>Send</code>, <code>Sync</code>, and <code>'static</code>, implement
<code>Fail</code> by a blanket impl.</p>
</div>
<h2 id='provided-methods' class='small-section-header'>
Provided Methods<a href='#provided-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='method.cause' class='method'><span id='cause.v' class='invisible'><code>fn <a href='#method.cause' class='fnname'>cause</a>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><&<a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a>></code></span></h3><div class='docblock'><p>Returns a reference to the underlying cause of this failure, if it
is an error that wraps other errors.</p>
<p>Returns <code>None</code> if this failure does not have another error as its
underlying cause. By default, this returns <code>None</code>.</p>
<p>This should <strong>never</strong> return a reference to <code>self</code>, but only return
<code>Some</code> when it can return a <strong>different</strong> failure. Users may loop
over the cause chain, and returning <code>self</code> would result in an infinite
loop.</p>
</div><h3 id='method.backtrace' class='method'><span id='backtrace.v' class='invisible'><code>fn <a href='#method.backtrace' class='fnname'>backtrace</a>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><&<a class="struct" href="../failure/struct.Backtrace.html" title="struct failure::Backtrace">Backtrace</a>></code></span></h3><div class='docblock'><p>Returns a reference to the <code>Backtrace</code> carried by this failure, if it
carries one.</p>
<p>Returns <code>None</code> if this failure does not carry a backtrace. By
default, this returns <code>None</code>.</p>
</div><h3 id='method.context' class='method'><span id='context.v' class='invisible'><code>fn <a href='#method.context' class='fnname'>context</a><D>(self, context: D) -> <a class="struct" href="../failure/struct.Context.html" title="struct failure::Context">Context</a><D> <span class="where fmt-newline">where<br> D: <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html" title="trait core::fmt::Display">Display</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + 'static,<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, </span></code></span></h3><div class='docblock'><p>Provides context for this failure.</p>
<p>This can provide additional information about this error, appropriate
to the semantics of the current layer. That is, if you have a
lower-level error, such as an IO error, you can provide additional context
about what that error means in the context of your function. This
gives users of this function more information about what has gone
wrong.</p>
<p>This takes any type that implements <code>Display</code>, as well as
<code>Send</code>/<code>Sync</code>/<code>'static</code>. In practice, this means it can take a <code>String</code>
or a string literal, or another failure, or some other custom context-carrying
type.</p>
</div><h3 id='method.compat' class='method'><span id='compat.v' class='invisible'><code>fn <a href='#method.compat' class='fnname'>compat</a>(self) -> <a class="struct" href="../failure/struct.Compat.html" title="struct failure::Compat">Compat</a><Self> <span class="where fmt-newline">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, </span></code></span></h3><div class='docblock'><p>Wraps this failure in a compatibility wrapper that implements
<code>std::error::Error</code>.</p>
<p>This allows failures to be compatible with older crates that
expect types that implement the <code>Error</code> trait from <code>std::error</code>.</p>
</div><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><'f></span></div><div class="content hidden"><h3 class="important">Important traits for <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><'f></h3><code class="content"><span class="where fmt-newline">impl<'f> <a class="trait" href="https://doc.rust-lang.org/nightly/core/iter/iterator/trait.Iterator.html" title="trait core::iter::iterator::Iterator">Iterator</a> for <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><'f></span><span class="where fmt-newline"> type <a href='https://doc.rust-lang.org/nightly/core/iter/iterator/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = &'f <a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a>;</span></code></div></div><h3 id='method.causes' class='method'><span id='causes.v' class='invisible'><code>fn <a href='#method.causes' class='fnname'>causes</a>(&self) -> <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a> <span class="where fmt-newline">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, </span></code></span></h3><div class='docblock'><p>Returns a iterator over the causes of this <code>Fail</code> with itself
as the first item and the <code>root_cause</code> as the final item.</p>
</div><h3 id='method.root_cause' class='method'><span id='root_cause.v' class='invisible'><code>fn <a href='#method.root_cause' class='fnname'>root_cause</a>(&self) -> &<a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a> <span class="where fmt-newline">where<br> Self: <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>, </span></code></span></h3><div class='docblock'><p>Returns the "root cause" of this <code>Fail</code> - the last value in the
cause chain which does not return an underlying <code>cause</code>.</p>
<p>If this type does not have a cause, <code>self</code> is returned, because
it is its own root cause.</p>
</div></div>
<h2 id='methods' class='small-section-header'>
Methods<a href='#methods' class='anchor'></a>
</h2>
<h3 id='impl' class='impl'><span class='in-band'><code>impl <a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a></code><a href='#impl' class='anchor'></a></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/failure/lib.rs.html#164-203' title='goto source code'>[src]</a></span></h3>
<div class='impl-items'><h4 id='method.downcast_ref' class="method"><span id='downcast_ref.v' class='invisible'><code>pub fn <a href='#method.downcast_ref' class='fnname'>downcast_ref</a><T: <a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a>>(&self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/failure/lib.rs.html#168-174' title='goto source code'>[src]</a></span></h4>
<div class='docblock'><p>Attempts to downcast this failure to a concrete type by reference.</p>
<p>If the underlying error is not of type <code>T</code>, this will return <code>None</code>.</p>
</div><h4 id='method.downcast_mut' class="method"><span id='downcast_mut.v' class='invisible'><code>pub fn <a href='#method.downcast_mut' class='fnname'>downcast_mut</a><T: <a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a>>(&mut self) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/option/enum.Option.html" title="enum core::option::Option">Option</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&mut </a>T></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/failure/lib.rs.html#180-186' title='goto source code'>[src]</a></span></h4>
<div class='docblock'><p>Attempts to downcast this failure to a concrete type by mutable
reference.</p>
<p>If the underlying error is not of type <code>T</code>, this will return <code>None</code>.</p>
</div><h4 id='method.root_cause-1' class="method"><span id='root_cause.v-1' class='invisible'><code>pub fn <a href='#method.root_cause-1' class='fnname'>root_cause</a>(&self) -> &<a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/failure/lib.rs.html#194-196' title='goto source code'>[src]</a></span></h4>
<div class='docblock'><p>Returns the "root cause" of this <code>Fail</code> - the last value in the
cause chain which does not return an underlying <code>cause</code>.</p>
<p>If this type does not have a cause, <code>self</code> is returned, because
it is its own root cause.</p>
</div><h4 id='method.causes-1' class="method"><div class="important-traits"><div class='tooltip'>ⓘ<span class='tooltiptext'>Important traits for <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><'f></span></div><div class="content hidden"><h3 class="important">Important traits for <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><'f></h3><code class="content"><span class="where fmt-newline">impl<'f> <a class="trait" href="https://doc.rust-lang.org/nightly/core/iter/iterator/trait.Iterator.html" title="trait core::iter::iterator::Iterator">Iterator</a> for <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a><'f></span><span class="where fmt-newline"> type <a href='https://doc.rust-lang.org/nightly/core/iter/iterator/trait.Iterator.html#associatedtype.Item' class="type">Item</a> = &'f <a class="trait" href="../failure/trait.Fail.html" title="trait failure::Fail">Fail</a>;</span></code></div></div><span id='causes.v-1' class='invisible'><code>pub fn <a href='#method.causes-1' class='fnname'>causes</a>(&self) -> <a class="struct" href="../failure/struct.Causes.html" title="struct failure::Causes">Causes</a></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../src/failure/lib.rs.html#200-202' title='goto source code'>[src]</a></span></h4>
<div class='docblock'><p>Returns a iterator over the causes of this <code>Fail</code> with itself
as the first item and the <code>root_cause</code> as the final item.</p>
</div></div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
<li><div class='out-of-band'><a class='srclink' href='../src/failure/context.rs.html#83-91' title='goto source code'>[src]</a></div><code>impl<D: <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Display.html" title="trait core::fmt::Display">Display</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + 'static> Fail for <a class="struct" href="../failure/struct.Context.html" title="struct failure::Context">Context</a><D></code></li>
<li><div class='out-of-band'><a class='srclink' href='../src/failure/sync_failure.rs.html#97' title='goto source code'>[src]</a></div><code>impl<E: <a class="trait" href="https://doc.rust-lang.org/nightly/std/error/trait.Error.html" title="trait std::error::Error">Error</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + 'static> Fail for <a class="struct" href="../failure/struct.SyncFailure.html" title="struct failure::SyncFailure">SyncFailure</a><E></code></li>
<li><div class='out-of-band'><a class='srclink' href='../src/failure/lib.rs.html#206' title='goto source code'>[src]</a></div><code>impl<E: <a class="trait" href="https://doc.rust-lang.org/nightly/std/error/trait.Error.html" title="trait std::error::Error">StdError</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a> + 'static> Fail for E</code></li>
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