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<!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="Extension trait adding combinators for working with types implementing `MakeWriter`."><title>MakeWriterExt in tracing_subscriber::fmt::writer - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-46f98efaafac5295.ttf.woff2,FiraSans-Regular-018c141bf0843ffd.woff2,FiraSans-Medium-8f9a781e4970d388.woff2,SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2,SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2" crossorigin href="../../../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../../../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../../../static.files/rustdoc-dd39b87e5fcfba68.css"><meta name="rustdoc-vars" data-root-path="../../../" data-static-root-path="../../../static.files/" data-current-crate="tracing_subscriber" data-themes="" data-resource-suffix="" data-rustdoc-version="1.80.0 (051478957 2024-07-21)" data-channel="1.80.0" data-search-js="search-d52510db62a78183.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../../../static.files/storage-118b08c4c78b968e.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../../static.files/main-20a3ad099b048cf2.js"></script><noscript><link rel="stylesheet" href="../../../static.files/noscript-df360f571f6edeae.css"></noscript><link rel="alternate icon" type="image/png" href="../../../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../../../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc trait"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button><a class="logo-container" href="../../../tracing_subscriber/index.html"><img src="https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png" alt=""></a></nav><nav class="sidebar"><div class="sidebar-crate"><a class="logo-container" href="../../../tracing_subscriber/index.html"><img src="https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png" alt="logo"></a><h2><a href="../../../tracing_subscriber/index.html">tracing_subscriber</a><span class="version">0.3.18</span></h2></div><h2 class="location"><a href="#">MakeWriterExt</a></h2><div class="sidebar-elems"><section><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.and">and</a></li><li><a href="#method.or_else">or_else</a></li><li><a href="#method.with_filter">with_filter</a></li><li><a href="#method.with_max_level">with_max_level</a></li><li><a href="#method.with_min_level">with_min_level</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In tracing_subscriber::fmt::writer</a></h2></div></nav><div class="sidebar-resizer"></div><main><div class="width-limiter"><rustdoc-search></rustdoc-search><section id="main-content" class="content"><div class="main-heading"><h1>Trait <a href="../../index.html">tracing_subscriber</a>::<wbr><a href="../index.html">fmt</a>::<wbr><a href="index.html">writer</a>::<wbr><a class="trait" href="#">MakeWriterExt</a><button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><span class="out-of-band"><a class="src" href="../../../src/tracing_subscriber/fmt/writer.rs.html#217-491">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><code>pub trait MakeWriterExt&lt;'a&gt;: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a&gt; {
// Provided methods
fn <a href="#method.with_max_level" class="fn">with_max_level</a>(self, level: <a class="struct" href="../../../tracing_core/metadata/struct.Level.html" title="struct tracing_core::metadata::Level">Level</a>) -&gt; <a class="struct" href="struct.WithMaxLevel.html" title="struct tracing_subscriber::fmt::writer::WithMaxLevel">WithMaxLevel</a>&lt;Self&gt;
<span class="where">where Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
<span class="item-spacer"></span> fn <a href="#method.with_min_level" class="fn">with_min_level</a>(self, level: <a class="struct" href="../../../tracing_core/metadata/struct.Level.html" title="struct tracing_core::metadata::Level">Level</a>) -&gt; <a class="struct" href="struct.WithMinLevel.html" title="struct tracing_subscriber::fmt::writer::WithMinLevel">WithMinLevel</a>&lt;Self&gt;
<span class="where">where Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
<span class="item-spacer"></span> fn <a href="#method.with_filter" class="fn">with_filter</a>&lt;F&gt;(self, filter: F) -&gt; <a class="struct" href="struct.WithFilter.html" title="struct tracing_subscriber::fmt::writer::WithFilter">WithFilter</a>&lt;Self, F&gt;
<span class="where">where Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
F: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&amp;<a class="struct" href="../../../tracing_core/metadata/struct.Metadata.html" title="struct tracing_core::metadata::Metadata">Metadata</a>&lt;'_&gt;) -&gt; <a class="primitive" href="https://doc.rust-lang.org/1.80.0/std/primitive.bool.html">bool</a></span> { ... }
<span class="item-spacer"></span> fn <a href="#method.and" class="fn">and</a>&lt;B&gt;(self, other: B) -&gt; <a class="struct" href="struct.Tee.html" title="struct tracing_subscriber::fmt::writer::Tee">Tee</a>&lt;Self, B&gt; <a href="#" class="tooltip" data-notable-ty="Tee&lt;Self, B&gt;"></a>
<span class="where">where Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
B: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a&gt; + <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span> { ... }
<span class="item-spacer"></span> fn <a href="#method.or_else" class="fn">or_else</a>&lt;W, B&gt;(self, other: B) -&gt; <a class="struct" href="struct.OrElse.html" title="struct tracing_subscriber::fmt::writer::OrElse">OrElse</a>&lt;Self, B&gt;
<span class="where">where Self: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a, Writer = <a class="type" href="type.OptionalWriter.html" title="type tracing_subscriber::fmt::writer::OptionalWriter">OptionalWriter</a>&lt;W&gt;&gt; + <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
B: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a&gt; + <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
W: <a class="trait" href="https://doc.rust-lang.org/1.80.0/std/io/trait.Write.html" title="trait std::io::Write">Write</a></span> { ... }
}</code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Extension trait adding combinators for working with types implementing
<a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>.</p>
<p>This is not intended to be implemented directly for user-defined
<a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>s; instead, it should be imported when the desired methods are
used.</p>
</div></details><h2 id="provided-methods" class="section-header">Provided Methods<a href="#provided-methods" class="anchor">§</a></h2><div class="methods"><details class="toggle method-toggle" open><summary><section id="method.with_max_level" class="method"><a class="src rightside" href="../../../src/tracing_subscriber/fmt/writer.rs.html#276-281">source</a><h4 class="code-header">fn <a href="#method.with_max_level" class="fn">with_max_level</a>(self, level: <a class="struct" href="../../../tracing_core/metadata/struct.Level.html" title="struct tracing_core::metadata::Level">Level</a>) -&gt; <a class="struct" href="struct.WithMaxLevel.html" title="struct tracing_subscriber::fmt::writer::WithMaxLevel">WithMaxLevel</a>&lt;Self&gt;<div class="where">where
Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Wraps <code>self</code> and returns a <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a> that will only write output
for events at or below the provided verbosity <a href="../../../tracing_core/metadata/struct.Level.html" title="struct tracing_core::metadata::Level"><code>Level</code></a>. For instance,
<code>Level::TRACE</code> is considered to be _more verbose<code>than</code>Level::INFO`.</p>
<p>Events whose level is more verbose than <code>level</code> will be ignored, and no
output will be written.</p>
<h5 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing::Level;
<span class="kw">use </span>tracing_subscriber::fmt::writer::MakeWriterExt;
<span class="comment">// Construct a writer that outputs events to `stderr` only if the span or
// event's level is &gt;= WARN (WARN and ERROR).
</span><span class="kw">let </span>mk_writer = std::io::stderr.with_max_level(Level::WARN);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
<p>Writing the <code>ERROR</code> and <code>WARN</code> levels to <code>stderr</code>, and everything else
to <code>stdout</code>:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code>
<span class="kw">let </span>mk_writer = std::io::stderr
.with_max_level(Level::WARN)
.or_else(std::io::stdout);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
<p>Writing the <code>ERROR</code> level to <code>stderr</code>, the <code>INFO</code> and <code>WARN</code> levels to
<code>stdout</code>, and the <code>INFO</code> and DEBUG` levels to a file:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::{sync::Arc, fs::File};
<span class="kw">let </span>debug_log = Arc::new(File::create(<span class="string">"debug.log"</span>)<span class="question-mark">?</span>);
<span class="kw">let </span>mk_writer = std::io::stderr
.with_max_level(Level::ERROR)
.or_else(std::io::stdout
.with_max_level(Level::INFO)
.and(debug_log.with_max_level(Level::DEBUG))
);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
</div></details><details class="toggle method-toggle" open><summary><section id="method.with_min_level" class="method"><a class="src rightside" href="../../../src/tracing_subscriber/fmt/writer.rs.html#318-323">source</a><h4 class="code-header">fn <a href="#method.with_min_level" class="fn">with_min_level</a>(self, level: <a class="struct" href="../../../tracing_core/metadata/struct.Level.html" title="struct tracing_core::metadata::Level">Level</a>) -&gt; <a class="struct" href="struct.WithMinLevel.html" title="struct tracing_subscriber::fmt::writer::WithMinLevel">WithMinLevel</a>&lt;Self&gt;<div class="where">where
Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Wraps <code>self</code> and returns a <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a> that will only write output
for events at or above the provided verbosity <a href="../../../tracing_core/metadata/struct.Level.html" title="struct tracing_core::metadata::Level"><code>Level</code></a>.</p>
<p>Events whose level is less verbose than <code>level</code> will be ignored, and no
output will be written.</p>
<h5 id="examples-1"><a class="doc-anchor" href="#examples-1">§</a>Examples</h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing::Level;
<span class="kw">use </span>tracing_subscriber::fmt::writer::MakeWriterExt;
<span class="comment">// Construct a writer that outputs events to `stdout` only if the span or
// event's level is &lt;= DEBUG (DEBUG and TRACE).
</span><span class="kw">let </span>mk_writer = std::io::stdout.with_min_level(Level::DEBUG);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
<p>This can be combined with <a href="trait.MakeWriterExt.html#method.with_max_level" title="method tracing_subscriber::fmt::writer::MakeWriterExt::with_max_level"><code>MakeWriterExt::with_max_level</code></a> to write
only within a range of levels:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// Only write the `DEBUG` and `INFO` levels to stdout.
</span><span class="kw">let </span>mk_writer = std::io::stdout
.with_max_level(Level::DEBUG)
.with_min_level(Level::INFO)
<span class="comment">// Write the `WARN` and `ERROR` levels to stderr.
</span>.and(std::io::stderr.with_min_level(Level::WARN));
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
</div></details><details class="toggle method-toggle" open><summary><section id="method.with_filter" class="method"><a class="src rightside" href="../../../src/tracing_subscriber/fmt/writer.rs.html#397-403">source</a><h4 class="code-header">fn <a href="#method.with_filter" class="fn">with_filter</a>&lt;F&gt;(self, filter: F) -&gt; <a class="struct" href="struct.WithFilter.html" title="struct tracing_subscriber::fmt::writer::WithFilter">WithFilter</a>&lt;Self, F&gt;<div class="where">where
Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
F: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(&amp;<a class="struct" href="../../../tracing_core/metadata/struct.Metadata.html" title="struct tracing_core::metadata::Metadata">Metadata</a>&lt;'_&gt;) -&gt; <a class="primitive" href="https://doc.rust-lang.org/1.80.0/std/primitive.bool.html">bool</a>,</div></h4></section></summary><div class="docblock"><p>Wraps <code>self</code> with a predicate that takes a span or events <a href="../../../tracing_core/metadata/struct.Metadata.html" title="struct tracing_core::metadata::Metadata"><code>Metadata</code></a>
and returns a <code>bool</code>. The returned <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>s
<a href="../trait.MakeWriter.html#method.make_writer_for" title="method tracing_subscriber::fmt::MakeWriter::make_writer_for"><code>MakeWriter::make_writer_for</code></a> method will check the predicate to
determine if a writer should be produced for a given span or event.</p>
<p>If the predicate returns <code>false</code>, the wrapped <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>s
<a href="../trait.MakeWriter.html#method.make_writer_for" title="method tracing_subscriber::fmt::MakeWriter::make_writer_for"><code>make_writer_for</code></a> will return <a href="enum.EitherWriter.html#method.none" title="associated function tracing_subscriber::fmt::writer::EitherWriter::none"><code>OptionalWriter::none</code></a>.
Otherwise, it calls the wrapped <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>s
<a href="../trait.MakeWriter.html#method.make_writer_for" title="method tracing_subscriber::fmt::MakeWriter::make_writer_for"><code>make_writer_for</code></a> method, and returns the produced writer.</p>
<p>This can be used to filter an output based on arbitrary <a href="../../../tracing_core/metadata/struct.Metadata.html" title="struct tracing_core::metadata::Metadata"><code>Metadata</code></a>
parameters.</p>
<h5 id="examples-2"><a class="doc-anchor" href="#examples-2">§</a>Examples</h5>
<p>Writing events with a specific target to an HTTP access log, and other
events to stdout:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing_subscriber::fmt::writer::MakeWriterExt;
<span class="kw">use </span>std::{sync::Arc, fs::File};
<span class="kw">let </span>access_log = Arc::new(File::create(<span class="string">"access.log"</span>)<span class="question-mark">?</span>);
<span class="kw">let </span>mk_writer = access_log
<span class="comment">// Only write events with the target "http::access_log" to the
// access log file.
</span>.with_filter(|meta| meta.target() == <span class="string">"http::access_log"</span>)
<span class="comment">// Write events with all other targets to stdout.
</span>.or_else(std::io::stdout);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
<p>Conditionally enabling or disabling a log file:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing_subscriber::fmt::writer::MakeWriterExt;
<span class="kw">use </span>std::{
sync::{Arc, atomic::{AtomicBool, Ordering}},
fs::File,
};
<span class="kw">static </span>DEBUG_LOG_ENABLED: AtomicBool = AtomicBool::new(<span class="bool-val">false</span>);
<span class="comment">// Create the debug log file
</span><span class="kw">let </span>debug_file = Arc::new(File::create(<span class="string">"debug.log"</span>)<span class="question-mark">?</span>)
<span class="comment">// Enable the debug log only if the flag is enabled.
</span>.with_filter(|<span class="kw">_</span>| DEBUG_LOG_ENABLED.load(Ordering::Acquire));
<span class="comment">// Always write to stdout
</span><span class="kw">let </span>mk_writer = std::io::stdout
<span class="comment">// Write to the debug file if it's enabled
</span>.and(debug_file);
tracing_subscriber::fmt().with_writer(mk_writer).init();
<span class="comment">// ...
// Later, we can toggle on or off the debug log file.
</span>DEBUG_LOG_ENABLED.store(<span class="bool-val">true</span>, Ordering::Release);</code></pre></div>
</div></details><details class="toggle method-toggle" open><summary><section id="method.and" class="method"><a class="src rightside" href="../../../src/tracing_subscriber/fmt/writer.rs.html#452-458">source</a><h4 class="code-header">fn <a href="#method.and" class="fn">and</a>&lt;B&gt;(self, other: B) -&gt; <a class="struct" href="struct.Tee.html" title="struct tracing_subscriber::fmt::writer::Tee">Tee</a>&lt;Self, B&gt; <a href="#" class="tooltip" data-notable-ty="Tee&lt;Self, B&gt;"></a><div class="where">where
Self: <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
B: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a&gt; + <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</div></h4></section></summary><div class="docblock"><p>Combines <code>self</code> with another type implementing <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>, returning
a new <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a> that produces <a href="https://doc.rust-lang.org/1.80.0/std/io/trait.Write.html" title="trait std::io::Write">writers</a> that write to <em>both</em>
outputs.</p>
<p>If writing to either writer returns an error, the returned writer will
return that error. However, both writers will still be written to before
the error is returned, so it is possible for one writer to fail while
the other is written to successfully.</p>
<h5 id="examples-3"><a class="doc-anchor" href="#examples-3">§</a>Examples</h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing_subscriber::fmt::writer::MakeWriterExt;
<span class="comment">// Construct a writer that outputs events to `stdout` *and* `stderr`.
</span><span class="kw">let </span>mk_writer = std::io::stdout.and(std::io::stderr);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
<p><code>and</code> can be used in conjunction with filtering combinators. For
example, if we want to write to a number of outputs depending on the
level of an event, we could write:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing::Level;
<span class="kw">use </span>std::{sync::Arc, fs::File};
<span class="kw">let </span>debug_log = Arc::new(File::create(<span class="string">"debug.log"</span>)<span class="question-mark">?</span>);
<span class="comment">// Write everything to the debug log.
</span><span class="kw">let </span>mk_writer = debug_log
<span class="comment">// Write the `ERROR` and `WARN` levels to stderr.
</span>.and(std::io::stderr.with_max_level(Level::WARN))
<span class="comment">// Write `INFO` to `stdout`.
</span>.and(std::io::stdout
.with_max_level(Level::INFO)
.with_min_level(Level::INFO)
);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
</div></details><details class="toggle method-toggle" open><summary><section id="method.or_else" class="method"><a class="src rightside" href="../../../src/tracing_subscriber/fmt/writer.rs.html#483-490">source</a><h4 class="code-header">fn <a href="#method.or_else" class="fn">or_else</a>&lt;W, B&gt;(self, other: B) -&gt; <a class="struct" href="struct.OrElse.html" title="struct tracing_subscriber::fmt::writer::OrElse">OrElse</a>&lt;Self, B&gt;<div class="where">where
Self: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a, Writer = <a class="type" href="type.OptionalWriter.html" title="type tracing_subscriber::fmt::writer::OptionalWriter">OptionalWriter</a>&lt;W&gt;&gt; + <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
B: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a&gt; + <a class="trait" href="https://doc.rust-lang.org/1.80.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,
W: <a class="trait" href="https://doc.rust-lang.org/1.80.0/std/io/trait.Write.html" title="trait std::io::Write">Write</a>,</div></h4></section></summary><div class="docblock"><p>Combines <code>self</code> with another type implementing <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a>, returning
a new <a href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter"><code>MakeWriter</code></a> that calls <code>other</code>s <a href="../trait.MakeWriter.html#tymethod.make_writer" title="method tracing_subscriber::fmt::MakeWriter::make_writer"><code>make_writer</code></a> if <code>self</code>s
<code>make_writer</code> returns <a href="enum.EitherWriter.html#method.none" title="associated function tracing_subscriber::fmt::writer::EitherWriter::none"><code>OptionalWriter::none</code></a>.</p>
<h5 id="examples-4"><a class="doc-anchor" href="#examples-4">§</a>Examples</h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tracing::Level;
<span class="kw">use </span>tracing_subscriber::fmt::writer::MakeWriterExt;
<span class="comment">// Produces a writer that writes to `stderr` if the level is &gt;= WARN,
// or returns `OptionalWriter::none()` otherwise.
</span><span class="kw">let </span>stderr = std::io::stderr.with_max_level(Level::WARN);
<span class="comment">// If the `stderr` `MakeWriter` is disabled by the max level filter,
// write to stdout instead:
</span><span class="kw">let </span>mk_writer = stderr.or_else(std::io::stdout);
tracing_subscriber::fmt().with_writer(mk_writer).init();</code></pre></div>
</div></details></div><h2 id="implementors" class="section-header">Implementors<a href="#implementors" class="anchor">§</a></h2><div id="implementors-list"><section id="impl-MakeWriterExt%3C'a%3E-for-M" class="impl"><a class="src rightside" href="../../../src/tracing_subscriber/fmt/writer.rs.html#1201">source</a><a href="#impl-MakeWriterExt%3C'a%3E-for-M" class="anchor">§</a><h3 class="code-header">impl&lt;'a, M&gt; <a class="trait" href="trait.MakeWriterExt.html" title="trait tracing_subscriber::fmt::writer::MakeWriterExt">MakeWriterExt</a>&lt;'a&gt; for M<div class="where">where
M: <a class="trait" href="../trait.MakeWriter.html" title="trait tracing_subscriber::fmt::MakeWriter">MakeWriter</a>&lt;'a&gt;,</div></h3></section></div><script src="../../../trait.impl/tracing_subscriber/fmt/writer/trait.MakeWriterExt.js" async></script><script type="text/json" id="notable-traits-data">{"Tee<Self, B>":"<h3>Notable traits for <code><a class=\"struct\" href=\"struct.Tee.html\" title=\"struct tracing_subscriber::fmt::writer::Tee\">Tee</a>&lt;A, B&gt;</code></h3><pre><code><div class=\"where\">impl&lt;A, B&gt; <a class=\"trait\" href=\"https://doc.rust-lang.org/1.80.0/std/io/trait.Write.html\" title=\"trait std::io::Write\">Write</a> for <a class=\"struct\" href=\"struct.Tee.html\" title=\"struct tracing_subscriber::fmt::writer::Tee\">Tee</a>&lt;A, B&gt;<div class=\"where\">where\n A: <a class=\"trait\" href=\"https://doc.rust-lang.org/1.80.0/std/io/trait.Write.html\" title=\"trait std::io::Write\">Write</a>,\n B: <a class=\"trait\" href=\"https://doc.rust-lang.org/1.80.0/std/io/trait.Write.html\" title=\"trait std::io::Write\">Write</a>,</div></div>"}</script></section></div></main></body></html>