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405 lines
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<!DOCTYPE html>
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<meta name="generator" content="rustdoc">
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<meta name="description" content="API documentation for the Rust `log` crate.">
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<meta name="keywords" content="rust, rustlang, rust-lang, log">
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<title>log - Rust</title>
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<link rel="stylesheet" type="text/css" href="../rustdoc.css">
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<link rel="stylesheet" type="text/css" href="../main.css">
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<body class="rustdoc">
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<!--[if lte IE 8]>
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This old browser is unsupported and will most likely display funky
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<nav class="sidebar">
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<a href='../log/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a>
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<p class='location'></p><script>window.sidebarCurrent = {name: 'log', ty: 'mod', relpath: '../'};</script>
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<input class="search-input" name="search"
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autocomplete="off"
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placeholder="Click or press ‘S’ to search, ‘?’ for more options…"
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type="search">
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</div>
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</form>
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</nav>
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<section id='main' class="content mod">
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<h1 class='fqn'><span class='in-band'>Crate <a class='mod' href=''>log</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 id='src-0' class='srclink' href='../src/log/lib.rs.html#11-1013' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>A lightweight logging facade.</p>
|
||
|
||
<p>A logging facade provides a single logging API that abstracts over the
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actual logging implementation. Libraries can use the logging API provided
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||
by this crate, and the consumer of those libraries can choose the logging
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||
framework that is most suitable for its use case.</p>
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||
|
||
<p>If no logging implementation is selected, the facade falls back to a "noop"
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||
implementation that ignores all log messages. The overhead in this case
|
||
is very small - just an integer load, comparison and jump.</p>
|
||
|
||
<p>A log request consists of a target, a level, and a body. A target is a
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||
string which defaults to the module path of the location of the log
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||
request, though that default may be overridden. Logger implementations
|
||
typically use the target to filter requests based on some user
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||
configuration.</p>
|
||
|
||
<h1 id='use' class='section-header'><a href='#use'>Use</a></h1>
|
||
<h2 id='in-libraries' class='section-header'><a href='#in-libraries'>In libraries</a></h2>
|
||
<p>Libraries should link only to the <code>log</code> crate, and use the provided
|
||
macros to log whatever information will be useful to downstream consumers.</p>
|
||
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<h3 id='examples' class='section-header'><a href='#examples'>Examples</a></h3>
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||
<pre class='rust rust-example-rendered'>
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||
<span class='attribute'>#[<span class='ident'>macro_use</span>]</span>
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<span class='kw'>extern</span> <span class='kw'>crate</span> <span class='ident'>log</span>;
|
||
|
||
<span class='kw'>pub</span> <span class='kw'>fn</span> <span class='ident'>shave_the_yak</span>(<span class='ident'>yak</span>: <span class='kw-2'>&</span><span class='ident'>Yak</span>) {
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<span class='macro'>info</span><span class='macro'>!</span>(<span class='ident'>target</span>: <span class='string'>"yak_events"</span>, <span class='string'>"Commencing yak shaving for {:?}"</span>, <span class='ident'>yak</span>);
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||
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<span class='kw'>loop</span> {
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<span class='kw'>match</span> <span class='ident'>find_a_razor</span>() {
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<span class='prelude-val'>Ok</span>(<span class='ident'>razor</span>) <span class='op'>=></span> {
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<span class='macro'>info</span><span class='macro'>!</span>(<span class='string'>"Razor located: {}"</span>, <span class='ident'>razor</span>);
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<span class='ident'>yak</span>.<span class='ident'>shave</span>(<span class='ident'>razor</span>);
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<span class='kw'>break</span>;
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||
}
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<span class='prelude-val'>Err</span>(<span class='ident'>err</span>) <span class='op'>=></span> {
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<span class='macro'>warn</span><span class='macro'>!</span>(<span class='string'>"Unable to locate a razor: {}, retrying"</span>, <span class='ident'>err</span>);
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||
}
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||
}
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||
}
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||
}</pre>
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<h2 id='in-executables' class='section-header'><a href='#in-executables'>In executables</a></h2>
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||
<p>Executables should choose a logging framework and initialize it early in the
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||
runtime of the program. Logging frameworks will typically include a
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||
function to do this. Any log messages generated before the framework is
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||
initialized will be ignored.</p>
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||
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||
<p>The executable itself may use the <code>log</code> crate to log as well.</p>
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||
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||
<h3 id='warning' class='section-header'><a href='#warning'>Warning</a></h3>
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||
<p>The logging system may only be initialized once.</p>
|
||
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||
<h3 id='examples-1' class='section-header'><a href='#examples-1'>Examples</a></h3>
|
||
<pre class='rust rust-example-rendered'>
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||
<span class='attribute'>#[<span class='ident'>macro_use</span>]</span>
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||
<span class='kw'>extern</span> <span class='kw'>crate</span> <span class='ident'>log</span>;
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<span class='kw'>extern</span> <span class='kw'>crate</span> <span class='ident'>my_logger</span>;
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||
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<span class='kw'>fn</span> <span class='ident'>main</span>() {
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<span class='ident'>my_logger</span>::<span class='ident'>init</span>();
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<span class='macro'>info</span><span class='macro'>!</span>(<span class='string'>"starting up"</span>);
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<span class='comment'>// ...</span>
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}</pre>
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||
<h1 id='logger-implementations' class='section-header'><a href='#logger-implementations'>Logger implementations</a></h1>
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<p>Loggers implement the <code>Log</code> trait. Here's a very basic example that simply
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logs all messages at the <code>Error</code>, <code>Warn</code> or <code>Info</code> levels to stdout:</p>
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||
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||
<pre class='rust rust-example-rendered'>
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<span class='kw'>extern</span> <span class='kw'>crate</span> <span class='ident'>log</span>;
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<span class='kw'>use</span> <span class='ident'>log</span>::{<span class='ident'>LogRecord</span>, <span class='ident'>LogLevel</span>, <span class='ident'>LogMetadata</span>};
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<span class='kw'>struct</span> <span class='ident'>SimpleLogger</span>;
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<span class='kw'>impl</span> <span class='ident'>log</span>::<span class='ident'>Log</span> <span class='kw'>for</span> <span class='ident'>SimpleLogger</span> {
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<span class='kw'>fn</span> <span class='ident'>enabled</span>(<span class='kw-2'>&</span><span class='self'>self</span>, <span class='ident'>metadata</span>: <span class='kw-2'>&</span><span class='ident'>LogMetadata</span>) <span class='op'>-></span> <span class='ident'>bool</span> {
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<span class='ident'>metadata</span>.<span class='ident'>level</span>() <span class='op'><=</span> <span class='ident'>LogLevel</span>::<span class='ident'>Info</span>
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||
}
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<span class='kw'>fn</span> <span class='ident'>log</span>(<span class='kw-2'>&</span><span class='self'>self</span>, <span class='ident'>record</span>: <span class='kw-2'>&</span><span class='ident'>LogRecord</span>) {
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<span class='kw'>if</span> <span class='self'>self</span>.<span class='ident'>enabled</span>(<span class='ident'>record</span>.<span class='ident'>metadata</span>()) {
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<span class='macro'>println</span><span class='macro'>!</span>(<span class='string'>"{} - {}"</span>, <span class='ident'>record</span>.<span class='ident'>level</span>(), <span class='ident'>record</span>.<span class='ident'>args</span>());
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||
}
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||
}
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||
}
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||
</pre>
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<p>Loggers are installed by calling the <code>set_logger</code> function. It takes a
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closure which is provided a <code>MaxLogLevel</code> token and returns a <code>Log</code> trait
|
||
object. The <code>MaxLogLevel</code> token controls the global maximum log level. The
|
||
logging facade uses this as an optimization to improve performance of log
|
||
messages at levels that are disabled. In the case of our example logger,
|
||
we'll want to set the maximum log level to <code>Info</code>, since we ignore any
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||
<code>Debug</code> or <code>Trace</code> level log messages. A logging framework should provide a
|
||
function that wraps a call to <code>set_logger</code>, handling initialization of the
|
||
logger:</p>
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||
|
||
<pre class='rust rust-example-rendered'>
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||
<span class='kw'>pub</span> <span class='kw'>fn</span> <span class='ident'>init</span>() <span class='op'>-></span> <span class='prelude-ty'>Result</span><span class='op'><</span>(), <span class='ident'>SetLoggerError</span><span class='op'>></span> {
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||
<span class='ident'>log</span>::<span class='ident'>set_logger</span>(<span class='op'>|</span><span class='ident'>max_log_level</span><span class='op'>|</span> {
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||
<span class='ident'>max_log_level</span>.<span class='ident'>set</span>(<span class='ident'>LogLevelFilter</span>::<span class='ident'>Info</span>);
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||
<span class='ident'>Box</span>::<span class='ident'>new</span>(<span class='ident'>SimpleLogger</span>)
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||
})
|
||
}</pre>
|
||
|
||
<h1 id='use-with-no_std' class='section-header'><a href='#use-with-no_std'>Use with <code>no_std</code></a></h1>
|
||
<p>To use the <code>log</code> crate without depending on <code>libstd</code>, you need to specify
|
||
<code>default-features = false</code> when specifying the dependency in <code>Cargo.toml</code>.
|
||
This makes no difference to libraries using <code>log</code> since the logging API
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||
remains the same. However executables will need to use the <code>set_logger_raw</code>
|
||
function to initialize a logger and the <code>shutdown_logger_raw</code> function to
|
||
shut down the global logger before exiting:</p>
|
||
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='kw'>pub</span> <span class='kw'>fn</span> <span class='ident'>init</span>() <span class='op'>-></span> <span class='prelude-ty'>Result</span><span class='op'><</span>(), <span class='ident'>SetLoggerError</span><span class='op'>></span> {
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||
<span class='kw'>unsafe</span> {
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||
<span class='ident'>log</span>::<span class='ident'>set_logger_raw</span>(<span class='op'>|</span><span class='ident'>max_log_level</span><span class='op'>|</span> {
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||
<span class='kw'>static</span> <span class='ident'>LOGGER</span>: <span class='ident'>SimpleLogger</span> <span class='op'>=</span> <span class='ident'>SimpleLogger</span>;
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||
<span class='ident'>max_log_level</span>.<span class='ident'>set</span>(<span class='ident'>LogLevelFilter</span>::<span class='ident'>Info</span>);
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||
<span class='kw-2'>&</span><span class='ident'>SimpleLogger</span>
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||
})
|
||
}
|
||
}
|
||
<span class='kw'>pub</span> <span class='kw'>fn</span> <span class='ident'>shutdown</span>() <span class='op'>-></span> <span class='prelude-ty'>Result</span><span class='op'><</span>(), <span class='ident'>ShutdownLoggerError</span><span class='op'>></span> {
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||
<span class='ident'>log</span>::<span class='ident'>shutdown_logger_raw</span>().<span class='ident'>map</span>(<span class='op'>|</span><span class='ident'>logger</span><span class='op'>|</span> {
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||
<span class='kw'>let</span> <span class='ident'>logger</span> <span class='op'>=</span> <span class='kw'>unsafe</span> { <span class='kw-2'>&</span><span class='op'>*</span>(<span class='ident'>logger</span> <span class='kw'>as</span> <span class='op'>*</span><span class='kw'>const</span> <span class='ident'>SimpleLogger</span>) };
|
||
<span class='ident'>logger</span>.<span class='ident'>flush</span>();
|
||
})
|
||
}</pre>
|
||
</div><h2 id='macros' class='section-header'><a href="#macros">Macros</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.debug!.html'
|
||
title='log::debug!'>debug!</a></td>
|
||
<td class='docblock short'>
|
||
<p>Logs a message at the debug level.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.error!.html'
|
||
title='log::error!'>error!</a></td>
|
||
<td class='docblock short'>
|
||
<p>Logs a message at the error level.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.info!.html'
|
||
title='log::info!'>info!</a></td>
|
||
<td class='docblock short'>
|
||
<p>Logs a message at the info level.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.log!.html'
|
||
title='log::log!'>log!</a></td>
|
||
<td class='docblock short'>
|
||
<p>The standard logging macro.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.log_enabled!.html'
|
||
title='log::log_enabled!'>log_enabled!</a></td>
|
||
<td class='docblock short'>
|
||
<p>Determines if a message logged at the specified level in that module will
|
||
be logged.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.trace!.html'
|
||
title='log::trace!'>trace!</a></td>
|
||
<td class='docblock short'>
|
||
<p>Logs a message at the trace level.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='macro' href='macro.warn!.html'
|
||
title='log::warn!'>warn!</a></td>
|
||
<td class='docblock short'>
|
||
<p>Logs a message at the warn level.</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.LogLocation.html'
|
||
title='log::LogLocation'>LogLocation</a></td>
|
||
<td class='docblock short'>
|
||
<p>The location of a log message.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='struct' href='struct.LogMetadata.html'
|
||
title='log::LogMetadata'>LogMetadata</a></td>
|
||
<td class='docblock short'>
|
||
<p>Metadata about a log message.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='struct' href='struct.LogRecord.html'
|
||
title='log::LogRecord'>LogRecord</a></td>
|
||
<td class='docblock short'>
|
||
<p>The "payload" of a log message.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='struct' href='struct.MaxLogLevelFilter.html'
|
||
title='log::MaxLogLevelFilter'>MaxLogLevelFilter</a></td>
|
||
<td class='docblock short'>
|
||
<p>A token providing read and write access to the global maximum log level
|
||
filter.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='struct' href='struct.SetLoggerError.html'
|
||
title='log::SetLoggerError'>SetLoggerError</a></td>
|
||
<td class='docblock short'>
|
||
<p>The type returned by <code>set_logger</code> if <code>set_logger</code> has already been called.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='struct' href='struct.ShutdownLoggerError.html'
|
||
title='log::ShutdownLoggerError'>ShutdownLoggerError</a></td>
|
||
<td class='docblock short'>
|
||
<p>The type returned by <code>shutdown_logger_raw</code> if <code>shutdown_logger_raw</code> has
|
||
already been called or if <code>set_logger_raw</code> has not been called yet.</p>
|
||
</td>
|
||
</tr></table><h2 id='enums' class='section-header'><a href="#enums">Enums</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class='enum' href='enum.LogLevel.html'
|
||
title='log::LogLevel'>LogLevel</a></td>
|
||
<td class='docblock short'>
|
||
<p>An enum representing the available verbosity levels of the logging framework</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='enum' href='enum.LogLevelFilter.html'
|
||
title='log::LogLevelFilter'>LogLevelFilter</a></td>
|
||
<td class='docblock short'>
|
||
<p>An enum representing the available verbosity level filters of the logging
|
||
framework.</p>
|
||
</td>
|
||
</tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class='trait' href='trait.Log.html'
|
||
title='log::Log'>Log</a></td>
|
||
<td class='docblock short'>
|
||
<p>A trait encapsulating the operations required of a logger</p>
|
||
</td>
|
||
</tr></table><h2 id='functions' class='section-header'><a href="#functions">Functions</a></h2>
|
||
<table>
|
||
<tr class=' module-item'>
|
||
<td><a class='fn' href='fn.max_log_level.html'
|
||
title='log::max_log_level'>max_log_level</a></td>
|
||
<td class='docblock short'>
|
||
<p>Returns the current maximum log level.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='fn' href='fn.set_logger.html'
|
||
title='log::set_logger'>set_logger</a></td>
|
||
<td class='docblock short'>
|
||
<p>Sets the global logger.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='fn' href='fn.set_logger_raw.html'
|
||
title='log::set_logger_raw'>set_logger_raw</a></td>
|
||
<td class='docblock short'>
|
||
<p>Sets the global logger from a raw pointer.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='fn' href='fn.shutdown_logger.html'
|
||
title='log::shutdown_logger'>shutdown_logger</a></td>
|
||
<td class='docblock short'>
|
||
<p>Shuts down the global logger.</p>
|
||
</td>
|
||
</tr>
|
||
<tr class=' module-item'>
|
||
<td><a class='fn' href='fn.shutdown_logger_raw.html'
|
||
title='log::shutdown_logger_raw'>shutdown_logger_raw</a></td>
|
||
<td class='docblock short'>
|
||
<p>Shuts down the global logger.</p>
|
||
</td>
|
||
</tr></table></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>?</dt>
|
||
<dd>Show this help dialog</dd>
|
||
<dt>S</dt>
|
||
<dd>Focus the search field</dd>
|
||
<dt>⇤</dt>
|
||
<dd>Move up in search results</dd>
|
||
<dt>⇥</dt>
|
||
<dd>Move down in search results</dd>
|
||
<dt>⏎</dt>
|
||
<dd>Go to active search result</dd>
|
||
<dt>+</dt>
|
||
<dd>Collapse/expand 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>
|
||
</div>
|
||
</div>
|
||
</aside>
|
||
|
||
|
||
|
||
<script>
|
||
window.rootPath = "../";
|
||
window.currentCrate = "log";
|
||
window.playgroundUrl = "";
|
||
</script>
|
||
<script src="../jquery.js"></script>
|
||
<script src="../main.js"></script>
|
||
|
||
<script defer src="../search-index.js"></script>
|
||
</body>
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