<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1.0"><metaname="generator"content="rustdoc"><metaname="description"content="Provides the current span context to a formatter."><title>FmtContext in tracing_subscriber::fmt - Rust</title><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><linkrel="stylesheet"href="../../static.files/normalize-76eba96aa4d2e634.css"><linkrel="stylesheet"href="../../static.files/rustdoc-5bc39a1768837dd0.css"><metaname="rustdoc-vars"data-root-path="../../"data-static-root-path="../../static.files/"data-current-crate="tracing_subscriber"data-themes=""data-resource-suffix=""data-rustdoc-version="1.77.0 (aedd173a2 2024-03-17)"data-channel="1.77.0"data-search-js="search-dd67cee4cfa65049.js"data-settings-js="settings-4313503d2e1961c2.js"><scriptsrc="../../static.files/storage-4c98445ec4002617.js"></script><scriptdefersrc="sidebar-items.js"></script><scriptdefersrc="../../static.files/main-48f368f3872407c8.js"></script><noscript><linkrel="stylesheet"href="../../static.files/noscript-04d5337699b92874.css"></noscript><linkrel="alternate icon"type="image/png"href="../../static.files/favicon-16x16-8b506e7a72182f1c.png"><linkrel="alternate icon"type="image/png"href="../../static.files/favicon-32x32-422f7d1d52889060.png"><linkrel="icon"type="image/svg+xml"href="../../static.files/favicon-2c020d218678b618.svg"></head><bodyclass="rustdoc struct"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><navclass="mobile-topbar"><buttonclass="sidebar-menu-toggle"title="show sidebar"></button><aclass="logo-container"href="../../tracing_subscriber/index.html"><imgsrc="https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png"alt=""></a></nav><navclass="sidebar"><divclass="sidebar-crate"><aclass="logo-container"href="../../tracing_subscriber/index.html"><imgsrc="https://raw.githubusercontent.com/tokio-rs/tracing/master/assets/logo-type.png"alt="logo"></a><h2><ahref="../../tracing_subscriber/index.html">tracing_subscriber</a><spanclass="version">0.3.18</span></h2></div><h2class="location"><ahref="#">FmtContext</a></h2><divclass="sidebar-elems"><section><h3><ahref="#implementations">Methods</a></h3><ulclass="block method"><li><ahref="#method.current_span">current_span</a></li><li><ahref="#method.event_scope">event_scope</a></li><li><ahref="#method.exists">exists</a></li><li><ahref="#method.field_format">field_format</a></li><li><ahref="#method.lookup_current">lookup_current</a></li><li><ahref="#method.metadata">metadata</a></li><li><ahref="#method.parent_span">parent_span</a></li><li><ahref="#method.span">span</a></li><li><ahref="#method.span_scope">span_scope</a></li><li><ahref="#method.visit_spans">visit_spans</a></li></ul><h3><ahref="#trait-implementations">Trait Implementations</a></h3><ulclass="block trait-implementation"><li><ahref="#impl-Debug-for-FmtContext%3C'a,+S,+N%3E">Debug</a></li><li><ahref="#impl-FormatFields%3C'writer%3E-for-FmtContext%3C'cx,+S,+N%3E">FormatFields<'writer></a></li></ul><h3><ahref="#synthetic-implementations">Auto Trait Implementations</a></h3><ulclass="block synthetic-implementation"><li><ahref="#impl-RefUnwindSafe-for-FmtContext%3C'a,+S,+N%3E">!RefUnwindSafe</a></li><li><ahref="#impl-Send-for-FmtContext%3C'a,+S,+N%3E">!Send</a></li><li>
<main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><divid="sidebar-button"tabindex="-1"><ahref="../../tracing_subscriber/all.html"title="show sidebar"></a></div><inputclass="search-input"name="search"aria-label="Run search in the documentation"autocomplete="off"spellcheck="false"placeholder="Click or press ‘S’ to search, ‘?’ for more options…"type="search"><divid="help-button"tabindex="-1"><ahref="../../help.html"title="help">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Struct <ahref="../index.html">tracing_subscriber</a>::<wbr><ahref="index.html">fmt</a>::<wbr><aclass="struct"href="#">FmtContext</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../../src/tracing_subscriber/fmt/fmt_layer.rs.html#1011-1015">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><code>pub struct FmtContext<'a, S, N> { <spanclass="comment">/* private fields */</span> }</code></pre><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>Provides the current span context to a formatter.</p>
F: <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/ops/function/trait.FnMut.html"title="trait core::ops::function::FnMut">FnMut</a>(&<aclass="struct"href="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">SpanRef</a><'_, S>) -><aclass="enum"href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.77.0/std/primitive.unit.html">()</a>, E>,</div></h4></section></summary><divclass="docblock"><p>Visits every span in the current context with a closure.</p>
S: for<'lookup><aclass="trait"href="../registry/trait.LookupSpan.html"title="trait tracing_subscriber::registry::LookupSpan">LookupSpan</a><'lookup>,</div></h4></section></summary><divclass="docblock"><p>Returns metadata for the span with the given <code>id</code>, if it exists.</p>
<p>If this returns <code>None</code>, then no span exists for that ID (either it has
S: for<'lookup><aclass="trait"href="../registry/trait.LookupSpan.html"title="trait tracing_subscriber::registry::LookupSpan">LookupSpan</a><'lookup>,</div></h4></section></summary><divclass="docblock"><p>Returns <ahref="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">stored data</a> for the span with the given <code>id</code>, if it exists.</p>
<p>If this returns <code>None</code>, then no span exists for that ID (either it has
S: for<'lookup><aclass="trait"href="../registry/trait.LookupSpan.html"title="trait tracing_subscriber::registry::LookupSpan">LookupSpan</a><'lookup>,</div></h4></section></summary><divclass="docblock"><p>Returns <code>true</code> if an active span exists for the given <code>Id</code>.</p>
S: for<'lookup><aclass="trait"href="../registry/trait.LookupSpan.html"title="trait tracing_subscriber::registry::LookupSpan">LookupSpan</a><'lookup>,</div></h4></section></summary><divclass="docblock"><p>Returns <ahref="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">stored data</a> for the span that the wrapped subscriber considers
to be the current.</p>
<p>If this returns <code>None</code>, then we are not currently within a span.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.current_span"class="method"><aclass="src rightside"href="../../src/tracing_subscriber/fmt/fmt_layer.rs.html#1110-1112">source</a><h4class="code-header">pub fn <ahref="#method.current_span"class="fn">current_span</a>(&self) -><aclass="struct"href="../../tracing_core/span/struct.Current.html"title="struct tracing_core::span::Current">Current</a></h4></section></summary><divclass="docblock"><p>Returns the current span for this formatter.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.parent_span"class="method"><aclass="src rightside"href="../../src/tracing_subscriber/fmt/fmt_layer.rs.html#1122-1124">source</a><h4class="code-header">pub fn <ahref="#method.parent_span"class="fn">parent_span</a>(&self) -><aclass="enum"href="https://doc.rust-lang.org/1.77.0/core/option/enum.Option.html"title="enum core::option::Option">Option</a><<aclass="struct"href="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">SpanRef</a><'_, S>></h4></section></summary><divclass="docblock"><p>Returns <ahref="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">stored data</a> for the parent span of the event currently being
S: for<'lookup><aclass="trait"href="../registry/trait.LookupSpan.html"title="trait tracing_subscriber::registry::LookupSpan">LookupSpan</a><'lookup>,</div></h4></section></summary><divclass="docblock"><p>Returns an iterator over the <ahref="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">stored data</a> for all the spans in the
current context, starting with the specified span and ending with the
root of the trace tree and ending with the current span.</p>
<p>This is equivalent to the <ahref="../layer/struct.Context.html#method.span_scope"title="method tracing_subscriber::layer::Context::span_scope"><code>Context::span_scope</code></a> method.</p>
S: for<'lookup><aclass="trait"href="../registry/trait.LookupSpan.html"title="trait tracing_subscriber::registry::LookupSpan">LookupSpan</a><'lookup>,</div></h4></section></summary><divclass="docblock"><p>Returns an iterator over the <ahref="../registry/struct.SpanRef.html"title="struct tracing_subscriber::registry::SpanRef">stored data</a> for all the spans in the
event’s span context, starting with its parent span and ending with the
root of the trace tree.</p>
<p>This is equivalent to calling the <ahref="../layer/struct.Context.html#method.event_scope"title="method tracing_subscriber::layer::Context::event_scope"><code>Context::event_scope</code></a> method and
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.field_format"class="method"><aclass="src rightside"href="../../src/tracing_subscriber/fmt/fmt_layer.rs.html#1197-1199">source</a><h4class="code-header">pub fn <ahref="#method.field_format"class="fn">field_format</a>(&self) -><aclass="primitive"href="https://doc.rust-lang.org/1.77.0/std/primitive.reference.html">&N</a></h4></section></summary><divclass="docblock"><p>Returns the <ahref="trait.FormatFields.html"title="trait tracing_subscriber::fmt::FormatFields">field formatter</a> configured by the subscriber invoking
) -><aclass="type"href="https://doc.rust-lang.org/1.77.0/core/fmt/type.Result.html"title="type core::fmt::Result">Result</a></h4></section></summary><divclass='docblock'>Format the provided <code>fields</code> to the provided <ahref="format/struct.Writer.html"title="struct tracing_subscriber::fmt::format::Writer"><code>Writer</code></a>, returning a result.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.add_fields"class="method trait-impl"><aclass="src rightside"href="../../src/tracing_subscriber/fmt/format/mod.rs.html#241-250">source</a><ahref="#method.add_fields"class="anchor">§</a><h4class="code-header">fn <ahref="trait.FormatFields.html#method.add_fields"class="fn">add_fields</a>(
</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-Instrument-for-T"class="impl"><aclass="src rightside"href="../../src/tracing/instrument.rs.html#325">source</a><ahref="#impl-Instrument-for-T"class="anchor">§</a><h3class="code-header">impl<T><aclass="trait"href="../../tracing/instrument/trait.Instrument.html"title="trait tracing::instrument::Instrument">Instrument</a> for T</h3></section></summary><divclass="impl-items"><detailsclass="toggle method-toggle"open><summary><sectionid="method.instrument"class="method trait-impl"><aclass="src rightside"href="../../src/tracing/instrument.rs.html#86">source</a><ahref="#method.instrument"class="anchor">§</a><h4class="code-header">fn <ahref="../../tracing/instrument/trait.Instrument.html#method.instrument"class="fn">instrument</a>(self, span: <aclass="struct"href="../../tracing/span/struct.Span.html"title="struct tracing::span::Span">Span</a>) -><aclass="struct"href="../../tracing/instrument/struct.Instrumented.html"title="struct tracing::instrument::Instrumented">Instrumented</a><Self></h4></section></summary><divclass='docblock'>Instruments this type with the provided <ahref="../../tracing/span/struct.Span.html"title="struct tracing::span::Span"><code>Span</code></a>, returning an
<code>Instrumented</code> wrapper. <ahref="../../tracing/instrument/trait.Instrument.html#method.instrument">Read more</a></div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.in_current_span"class="method trait-impl"><aclass="src rightside"href="../../src/tracing/instrument.rs.html#128">source</a><ahref="#method.in_current_span"class="anchor">§</a><h4class="code-header">fn <ahref="../../tracing/instrument/trait.Instrument.html#method.in_current_span"class="fn">in_current_span</a>(self) -><aclass="struct"href="../../tracing/instrument/struct.Instrumented.html"title="struct tracing::instrument::Instrumented">Instrumented</a><Self></h4></section></summary><divclass='docblock'>Instruments this type with the <ahref="../../tracing/span/struct.Span.html#method.current"title="associated function tracing::span::Span::current">current</a><ahref="../../tracing/span/struct.Span.html"title="struct tracing::span::Span"><code>Span</code></a>, returning an
<code><ahref="https://doc.rust-lang.org/1.77.0/core/convert/trait.From.html"title="trait core::convert::From">From</a><T> for U</code> chooses to do.</p>
</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-TryFrom%3CU%3E-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.77.0/src/core/convert/mod.rs.html#804-806">source</a><ahref="#impl-TryFrom%3CU%3E-for-T"class="anchor">§</a><h3class="code-header">impl<T, U><aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><U> for T<divclass="where">where
U: <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.Into.html"title="trait core::convert::Into">Into</a><T>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Error-1"class="associatedtype trait-impl"><ahref="#associatedtype.Error-1"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html#associatedtype.Error"class="associatedtype">Error</a> = <aclass="enum"href="https://doc.rust-lang.org/1.77.0/core/convert/enum.Infallible.html"title="enum core::convert::Infallible">Infallible</a></h4></section></summary><divclass='docblock'>The type returned in the event of a conversion error.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.try_from"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.77.0/src/core/convert/mod.rs.html#811">source</a><ahref="#method.try_from"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html#tymethod.try_from"class="fn">try_from</a>(value: U) -><aclass="enum"href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><T, <T as <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><U>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a>></h4></section></summary><divclass='docblock'>Performs the conversion.</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-TryInto%3CU%3E-for-T"class="impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.77.0/src/core/convert/mod.rs.html#789-791">source</a><ahref="#impl-TryInto%3CU%3E-for-T"class="anchor">§</a><h3class="code-header">impl<T, U><aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryInto.html"title="trait core::convert::TryInto">TryInto</a><U> for T<divclass="where">where
U: <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>,</div></h3></section></summary><divclass="impl-items"><detailsclass="toggle"open><summary><sectionid="associatedtype.Error"class="associatedtype trait-impl"><ahref="#associatedtype.Error"class="anchor">§</a><h4class="code-header">type <ahref="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryInto.html#associatedtype.Error"class="associatedtype">Error</a> = <U as <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a></h4></section></summary><divclass='docblock'>The type returned in the event of a conversion error.</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.try_into"class="method trait-impl"><aclass="src rightside"href="https://doc.rust-lang.org/1.77.0/src/core/convert/mod.rs.html#796">source</a><ahref="#method.try_into"class="anchor">§</a><h4class="code-header">fn <ahref="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryInto.html#tymethod.try_into"class="fn">try_into</a>(self) -><aclass="enum"href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><U, <U as <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html"title="trait core::convert::TryFrom">TryFrom</a><T>>::<aclass="associatedtype"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.TryFrom.html#associatedtype.Error"title="type core::convert::TryFrom::Error">Error</a>></h4></section></summary><divclass='docblock'>Performs the conversion.</div></details></div></details><detailsclass="toggle implementors-toggle"><summary><sectionid="impl-WithSubscriber-for-T"class="impl"><aclass="src rightside"href="../../src/tracing/instrument.rs.html#393">source</a><ahref="#impl-WithSubscriber-for-T"class="anchor">§</a><h3class="code-header">impl<T><aclass="trait"href="../../tracing/instrument/trait.WithSubscriber.html"title="trait tracing::instrument::WithSubscriber">WithSubscriber</a> for T</h3></section></summary><divclass="impl-items"><detailsclass="toggle method-toggle"open><summary><sectionid="method.with_subscriber"class="method trait-impl"><aclass="src rightside"href="../../src/tracing/instrument.rs.html#176-178">source</a><ahref="#method.with_subscriber"class="anchor">§</a><h4class="code-header">fn <ahref="../../tracing/instrument/trait.WithSubscriber.html#method.with_subscriber"class="fn">with_subscriber</a><S>(self, subscriber: S) -><aclass="struct"href="../../tracing/instrument/struct.WithDispatch.html"title="struct tracing::instrument::WithDispatch">WithDispatch</a><Self><divclass="where">where
S: <aclass="trait"href="https://doc.rust-lang.org/1.77.0/core/convert/trait.Into.html"title="trait core::convert::Into">Into</a><<aclass="struct"href="../../tracing_core/dispatcher/struct.Dispatch.html"title="struct tracing_core::dispatcher::Dispatch">Dispatch</a>>,</div></h4></section></summary><divclass='docblock'>Attaches the provided <ahref="../../tracing_core/subscriber/trait.Subscriber.html"title="trait tracing_core::subscriber::Subscriber"><code>Subscriber</code></a> to this type, returning a
<ahref="../../tracing/instrument/struct.WithDispatch.html"title="struct tracing::instrument::WithDispatch"><code>WithDispatch</code></a> wrapper. <ahref="../../tracing/instrument/trait.WithSubscriber.html#method.with_subscriber">Read more</a></div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.with_current_subscriber"class="method trait-impl"><aclass="src rightside"href="../../src/tracing/instrument.rs.html#228">source</a><ahref="#method.with_current_subscriber"class="anchor">§</a><h4class="code-header">fn <ahref="../../tracing/instrument/trait.WithSubscriber.html#method.with_current_subscriber"class="fn">with_current_subscriber</a>(self) -><aclass="struct"href="../../tracing/instrument/struct.WithDispatch.html"title="struct tracing::instrument::WithDispatch">WithDispatch</a><Self></h4></section></summary><divclass='docblock'>Attaches the current <ahref="../../tracing/dispatcher/index.html#setting-the-default-subscriber"title="mod tracing::dispatcher">default</a><ahref="../../tracing_core/subscriber/trait.Subscriber.html"title="trait tracing_core::subscriber::Subscriber"><code>Subscriber</code></a> to this type, returning a
