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381 lines
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<meta name="keywords" content="rust, rustlang, rust-lang, quick_error">
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<title>quick_error - Rust</title>
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<div class="sidebar-menu">☰</div>
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<p class='location'>Crate quick_error</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#macros">Macros</a></li><li><a href="#structs">Structs</a></li><li><a href="#traits">Traits</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'quick_error', ty: 'mod', relpath: '../'};</script></div>
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<section id='main' class="content"><h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>quick_error</a></span><span class='out-of-band'><span id='render-detail'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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[<span class='inner'>−</span>]
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</a>
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</span><a class='srclink' href='../src/quick_error/lib.rs.html#1-1309' title='goto source code'>[src]</a></span></h1><div class='docblock'><p>A macro which makes errors easy to write</p>
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<p>Minimum type is like this:</p>
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|
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<pre class="rust rust-example-rendered">
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<span class="attribute">#[<span class="ident">macro_use</span>]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">quick_error</span>;
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|
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<span class="macro">quick_error</span><span class="macro">!</span> {
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
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<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
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<span class="ident">Variant1</span> {}
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}
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}</pre>
|
||
<p>Both <code>pub</code> and non-public types may be declared, and all meta attributes
|
||
(such as <code>#[derive(Debug)]</code>) are forwarded as is. The <code>Debug</code> must be
|
||
implemented (but you may do that yourself if you like). The documentation
|
||
comments <code>/// something</code> (as well as other meta attrbiutes) on variants
|
||
are allowed.</p>
|
||
<h1 id="allowed-syntax" class="section-header"><a href="#allowed-syntax">Allowed Syntax</a></h1>
|
||
<p>You may add arbitrary parameters to any struct variant:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
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||
<span class="macro">quick_error</span><span class="macro">!</span> {
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||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
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||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
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||
<span class="doccomment">/// IO Error</span>
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||
<span class="ident">Io</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) {}
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<span class="doccomment">/// Utf8 Error</span>
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<span class="ident">Utf8</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">str</span>::<span class="ident">Utf8Error</span>) {}
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||
}
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}</pre>
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<p>Note unlike in normal Enum declarations you declare names of fields (which
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are omitted from type). How they can be used is outlined below.</p>
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<p>Now you might have noticed trailing braces <code>{}</code>. They are used to define
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implementations. By default:</p>
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<ul>
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<li><code>Error::description()</code> returns variant name as static string</li>
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<li><code>Error::cause()</code> returns None (even if type wraps some value)</li>
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||
<li><code>Display</code> outputs <code>description()</code></li>
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<li>No <code>From</code> implementations are defined</li>
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||
</ul>
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||
<p>To define description simply add <code>description(value)</code> inside braces:</p>
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||
|
||
<pre class="rust rust-example-rendered">
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||
<span class="macro">quick_error</span><span class="macro">!</span> {
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
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<span class="ident">Io</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) {
|
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<span class="ident">description</span>(<span class="ident">err</span>.<span class="ident">description</span>())
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}
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<span class="ident">Utf8</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">str</span>::<span class="ident">Utf8Error</span>) {
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<span class="ident">description</span>(<span class="string">"utf8 error"</span>)
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}
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}
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}</pre>
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<p>Normal rules for borrowing apply. So most of the time description either
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returns constant string or forwards description from enclosed type.</p>
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<p>To change <code>cause</code> method to return some error, add <code>cause(value)</code>, for
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||
example:</p>
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<pre class="rust rust-example-rendered">
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<span class="macro">quick_error</span><span class="macro">!</span> {
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
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<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
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<span class="ident">Io</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) {
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<span class="ident">cause</span>(<span class="ident">err</span>)
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<span class="ident">description</span>(<span class="ident">err</span>.<span class="ident">description</span>())
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}
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<span class="ident">Utf8</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">str</span>::<span class="ident">Utf8Error</span>) {
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<span class="ident">description</span>(<span class="string">"utf8 error"</span>)
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}
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<span class="ident">Other</span>(<span class="ident">err</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span><span class="op">></span>) {
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<span class="ident">cause</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="ident">err</span>)
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<span class="ident">description</span>(<span class="ident">err</span>.<span class="ident">description</span>())
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}
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}
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}</pre>
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<p>Note you don't need to wrap value in <code>Some</code>, its implicit. In case you want
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<code>None</code> returned just omit the <code>cause</code>. You can't return <code>None</code>
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conditionally.</p>
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<p>To change how each clause is <code>Display</code>ed add <code>display(pattern,..args)</code>,
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for example:</p>
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<pre class="rust rust-example-rendered">
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||
<span class="macro">quick_error</span><span class="macro">!</span> {
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
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<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
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<span class="ident">Io</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) {
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<span class="ident">display</span>(<span class="string">"I/O error: {}"</span>, <span class="ident">err</span>)
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||
}
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<span class="ident">Utf8</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">str</span>::<span class="ident">Utf8Error</span>) {
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<span class="ident">display</span>(<span class="string">"Utf8 error, valid up to {}"</span>, <span class="ident">err</span>.<span class="ident">valid_up_to</span>())
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}
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}
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||
}</pre>
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<p>If you need a reference to the error when <code>Display</code>ing, you can instead use
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<code>display(x) -> (pattern, ..args)</code>, where <code>x</code> sets the name of the reference.</p>
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||
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||
<pre class="rust rust-example-rendered">
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||
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">error</span>::<span class="ident">Error</span>; <span class="comment">// put methods like `description()` of this trait into scope</span>
|
||
|
||
<span class="macro">quick_error</span><span class="macro">!</span> {
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||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
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||
<span class="ident">Io</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) {
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||
<span class="ident">display</span>(<span class="ident">x</span>) <span class="op">-></span> (<span class="string">"{}: {}"</span>, <span class="ident">x</span>.<span class="ident">description</span>(), <span class="ident">err</span>)
|
||
}
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||
<span class="ident">Utf8</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">str</span>::<span class="ident">Utf8Error</span>) {
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||
<span class="ident">display</span>(<span class="ident">self_</span>) <span class="op">-></span> (<span class="string">"{}, valid up to {}"</span>, <span class="ident">self_</span>.<span class="ident">description</span>(), <span class="ident">err</span>.<span class="ident">valid_up_to</span>())
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||
}
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||
}
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||
}</pre>
|
||
<p>To convert to the type from any other, use one of the three forms of
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<code>from</code> clause.</p>
|
||
<p>For example, to convert simple wrapper use bare <code>from()</code>:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="macro">quick_error</span><span class="macro">!</span> {
|
||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
|
||
<span class="ident">Io</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) {
|
||
<span class="ident">from</span>()
|
||
}
|
||
}
|
||
}</pre>
|
||
<p>This implements <code>From<io::Error></code>.</p>
|
||
<p>To convert to singleton enumeration type (discarding the value), use
|
||
the <code>from(type)</code> form:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="macro">quick_error</span><span class="macro">!</span> {
|
||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
|
||
<span class="ident">FormatError</span> {
|
||
<span class="ident">from</span>(<span class="ident">std</span>::<span class="ident">fmt</span>::<span class="ident">Error</span>)
|
||
}
|
||
}
|
||
}</pre>
|
||
<p>And the most powerful form is <code>from(var: type) -> (arguments...)</code>. It
|
||
might be used to convert to type with multiple arguments or for arbitrary
|
||
value conversions:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="macro">quick_error</span><span class="macro">!</span> {
|
||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">SomeError</span> {
|
||
<span class="ident">FailedOperation</span>(<span class="ident">s</span>: <span class="kw-2">&</span><span class="lifetime">'static</span> <span class="ident">str</span>, <span class="ident">errno</span>: <span class="ident">i32</span>) {
|
||
<span class="ident">from</span>(<span class="ident">errno</span>: <span class="ident">i32</span>) <span class="op">-></span> (<span class="string">"os error"</span>, <span class="ident">errno</span>)
|
||
<span class="ident">from</span>(<span class="ident">e</span>: <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>) <span class="op">-></span> (<span class="string">"io error"</span>, <span class="ident">e</span>.<span class="ident">raw_os_error</span>().<span class="ident">unwrap</span>())
|
||
}
|
||
<span class="doccomment">/// Converts from both kinds of utf8 errors</span>
|
||
<span class="ident">Utf8</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">str</span>::<span class="ident">Utf8Error</span>) {
|
||
<span class="ident">from</span>()
|
||
<span class="ident">from</span>(<span class="ident">err</span>: <span class="ident">std</span>::<span class="ident">string</span>::<span class="ident">FromUtf8Error</span>) <span class="op">-></span> (<span class="ident">err</span>.<span class="ident">utf8_error</span>())
|
||
}
|
||
}
|
||
}</pre>
|
||
<h1 id="context" class="section-header"><a href="#context">Context</a></h1>
|
||
<p>Since quick-error 1.1 we also have a <code>context</code> declaration, which is
|
||
similar to (the longest form of) <code>from</code>, but allows adding some context to
|
||
the error. We need a longer example to demonstrate this:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="kw">use</span> <span class="ident">quick_error</span>::<span class="ident">ResultExt</span>;
|
||
|
||
<span class="macro">quick_error</span><span class="macro">!</span> {
|
||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">Error</span> {
|
||
<span class="ident">File</span>(<span class="ident">filename</span>: <span class="ident">PathBuf</span>, <span class="ident">err</span>: <span class="ident">io</span>::<span class="ident">Error</span>) {
|
||
<span class="ident">context</span>(<span class="ident">path</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">Path</span>, <span class="ident">err</span>: <span class="ident">io</span>::<span class="ident">Error</span>)
|
||
<span class="op">-></span> (<span class="ident">path</span>.<span class="ident">to_path_buf</span>(), <span class="ident">err</span>)
|
||
}
|
||
}
|
||
}
|
||
|
||
<span class="kw">fn</span> <span class="ident">openfile</span>(<span class="ident">path</span>: <span class="kw-2">&</span><span class="ident">Path</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> {
|
||
<span class="macro">try</span><span class="macro">!</span>(<span class="ident">File</span>::<span class="ident">open</span>(<span class="ident">path</span>).<span class="ident">context</span>(<span class="ident">path</span>));
|
||
|
||
<span class="comment">// If we didn't have context, the line above would be written as;</span>
|
||
<span class="comment">//</span>
|
||
<span class="comment">// try!(File::open(path)</span>
|
||
<span class="comment">// .map_err(|err| Error::File(path.to_path_buf(), err)));</span>
|
||
|
||
<span class="prelude-val">Ok</span>(())
|
||
}
|
||
</pre>
|
||
<p>Each <code>context(a: A, b: B)</code> clause implements
|
||
<code>From<Context<A, B>> for Error</code>. Which means multiple <code>context</code> clauses
|
||
are a subject to the normal coherence rules. Unfortunately, we can't
|
||
provide full support of generics for the context, but you may either use a
|
||
lifetime <code>'a</code> for references or <code>AsRef<Type></code> (the latter means <code>A: AsRef<Type></code>, and <code>Type</code> must be concrete). It's also occasionally useful
|
||
to use a tuple as a type of the first argument.</p>
|
||
<p>You also need to <code>use quick_error::ResultExt</code> extension trait to get
|
||
working <code>.context()</code> method.</p>
|
||
<p>More info on context in <a href="http://bit.ly/1PsuxDt">this article</a>.</p>
|
||
<p>All forms of <code>from</code>, <code>display</code>, <code>description</code>, <code>cause</code>, and <code>context</code>
|
||
clauses can be combined and put in arbitrary order. Only <code>from</code> and
|
||
<code>context</code> can be used multiple times in single variant of enumeration.
|
||
Docstrings are also okay. Empty braces can be omitted as of quick_error
|
||
0.1.3.</p>
|
||
<h1 id="private-enums" class="section-header"><a href="#private-enums">Private Enums</a></h1>
|
||
<p>Since quick-error 1.2.0 we have a way to make a private enum that is
|
||
wrapped by public structure:</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
<span class="attribute">#[<span class="ident">macro_use</span>]</span> <span class="kw">extern</span> <span class="kw">crate</span> <span class="ident">quick_error</span>;
|
||
|
||
<span class="macro">quick_error</span><span class="macro">!</span> {
|
||
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
|
||
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">PubError</span> <span class="ident">wraps</span> <span class="ident">ErrorEnum</span> {
|
||
<span class="ident">Variant1</span> {}
|
||
}
|
||
}</pre>
|
||
<p>This generates data structures like this</p>
|
||
|
||
<pre class="rust rust-example-rendered">
|
||
|
||
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">PubError</span>(<span class="ident">ErrorEnum</span>);
|
||
|
||
<span class="kw">enum</span> <span class="ident">ErrorEnum</span> {
|
||
<span class="ident">Variant1</span>,
|
||
}
|
||
</pre>
|
||
<p>Which in turn allows you to export just <code>PubError</code> in your crate and keep
|
||
actual enumeration private to the crate. This is useful to keep backwards
|
||
compatibility for error types. Currently there is no shorcuts to define
|
||
error constructors for the inner type, but we consider adding some in
|
||
future versions.</p>
|
||
<p>It's possible to declare internal enum as public too.</p>
|
||
</div><h2 id='macros' class='section-header'><a href="#macros">Macros</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class="macro" href="macro.quick_error.html"
|
||
title='macro quick_error::quick_error'>quick_error</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Main macro that does all the work</p>
|
||
|
||
</td>
|
||
</tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class="struct" href="struct.Context.html"
|
||
title='struct quick_error::Context'>Context</a></td>
|
||
<td class='docblock-short'>
|
||
<p>Generic context type</p>
|
||
|
||
</td>
|
||
</tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
|
||
<table>
|
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|
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<p>Result extension trait adding a <code>context</code> method</p>
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Search functions by type signature (e.g.
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