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| </pre><pre class="rust"><code><span class="doccomment">//! `Span` and `Event` key-value data. |
| //! |
| //! Spans and events may be annotated with key-value data, referred to as known |
| //! as _fields_. These fields consist of a mapping from a key (corresponding to |
| //! a `&str` but represented internally as an array index) to a [`Value`]. |
| //! |
| //! # `Value`s and `Subscriber`s |
| //! |
| //! `Subscriber`s consume `Value`s as fields attached to [span]s or [`Event`]s. |
| //! The set of field keys on a given span or is defined on its [`Metadata`]. |
| //! When a span is created, it provides [`Attributes`] to the `Subscriber`'s |
| //! [`new_span`] method, containing any fields whose values were provided when |
| //! the span was created; and may call the `Subscriber`'s [`record`] method |
| //! with additional [`Record`]s if values are added for more of its fields. |
| //! Similarly, the [`Event`] type passed to the subscriber's [`event`] method |
| //! will contain any fields attached to each event. |
| //! |
| //! `tracing` represents values as either one of a set of Rust primitives |
| //! (`i64`, `u64`, `f64`, `bool`, and `&str`) or using a `fmt::Display` or |
| //! `fmt::Debug` implementation. `Subscriber`s are provided these primitive |
| //! value types as `dyn Value` trait objects. |
| //! |
| //! These trait objects can be formatted using `fmt::Debug`, but may also be |
| //! recorded as typed data by calling the [`Value::record`] method on these |
| //! trait objects with a _visitor_ implementing the [`Visit`] trait. This trait |
| //! represents the behavior used to record values of various types. For example, |
| //! an implementation of `Visit` might record integers by incrementing counters |
| //! for their field names rather than printing them. |
| //! |
| //! |
| //! # Using `valuable` |
| //! |
| //! `tracing`'s [`Value`] trait is intentionally minimalist: it supports only a small |
| //! number of Rust primitives as typed values, and only permits recording |
| //! user-defined types with their [`fmt::Debug`] or [`fmt::Display`] |
| //! implementations. However, there are some cases where it may be useful to record |
| //! nested values (such as arrays, `Vec`s, or `HashMap`s containing values), or |
| //! user-defined `struct` and `enum` types without having to format them as |
| //! unstructured text. |
| //! |
| //! To address `Value`'s limitations, `tracing` offers experimental support for |
| //! the [`valuable`] crate, which provides object-safe inspection of structured |
| //! values. User-defined types can implement the [`valuable::Valuable`] trait, |
| //! and be recorded as a `tracing` field by calling their [`as_value`] method. |
| //! If the [`Subscriber`] also supports the `valuable` crate, it can |
| //! then visit those types fields as structured values using `valuable`. |
| //! |
| //! <pre class="ignore" style="white-space:normal;font:inherit;"> |
| //! <strong>Note</strong>: <code>valuable</code> support is an |
| //! <a href = "../index.html#unstable-features">unstable feature</a>. See |
| //! the documentation on unstable features for details on how to enable it. |
| //! </pre> |
| //! |
| //! For example: |
| //! ```ignore |
| //! // Derive `Valuable` for our types: |
| //! use valuable::Valuable; |
| //! |
| //! #[derive(Clone, Debug, Valuable)] |
| //! struct User { |
| //! name: String, |
| //! age: u32, |
| //! address: Address, |
| //! } |
| //! |
| //! #[derive(Clone, Debug, Valuable)] |
| //! struct Address { |
| //! country: String, |
| //! city: String, |
| //! street: String, |
| //! } |
| //! |
| //! let user = User { |
| //! name: "Arwen Undomiel".to_string(), |
| //! age: 3000, |
| //! address: Address { |
| //! country: "Middle Earth".to_string(), |
| //! city: "Rivendell".to_string(), |
| //! street: "leafy lane".to_string(), |
| //! }, |
| //! }; |
| //! |
| //! // Recording `user` as a `valuable::Value` will allow the `tracing` subscriber |
| //! // to traverse its fields as a nested, typed structure: |
| //! tracing::info!(current_user = user.as_value()); |
| //! ``` |
| //! |
| //! Alternatively, the [`valuable()`] function may be used to convert a type |
| //! implementing [`Valuable`] into a `tracing` field value. |
| //! |
| //! When the `valuable` feature is enabled, the [`Visit`] trait will include an |
| //! optional [`record_value`] method. `Visit` implementations that wish to |
| //! record `valuable` values can implement this method with custom behavior. |
| //! If a visitor does not implement `record_value`, the [`valuable::Value`] will |
| //! be forwarded to the visitor's [`record_debug`] method. |
| //! |
| //! [`fmt::Debug`]: std::fmt::Debug |
| //! [`fmt::Display`]: std::fmt::Debug |
| //! [`valuable`]: https://crates.io/crates/valuable |
| //! [`valuable::Valuable`]: https://docs.rs/valuable/latest/valuable/trait.Valuable.html |
| //! [`as_value`]: https://docs.rs/valuable/latest/valuable/trait.Valuable.html#tymethod.as_value |
| //! [`valuable::Value`]: https://docs.rs/valuable/latest/valuable/enum.Value.html |
| //! [`Subscriber`]: crate::Subscriber |
| //! [`record_value`]: Visit::record_value |
| //! [`record_debug`]: Visit::record_debug |
| //! [span]: mod@crate::span |
| //! [`Event`]: crate::event::Event |
| //! [`Metadata`]: crate::Metadata |
| //! [`Attributes`]: crate::span::Attributes |
| //! [`Record`]: crate::span::Record |
| //! [`new_span`]: crate::Subscriber::new_span |
| //! [`record`]: crate::Subscriber::record |
| //! [`event`]: crate::Subscriber::event |
| </span><span class="kw">pub use </span>tracing_core::field::<span class="kw-2">*</span>; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::Metadata; |
| |
| <span class="doccomment">/// Trait implemented to allow a type to be used as a field key. |
| /// |
| /// <pre class="ignore" style="white-space:normal;font:inherit;"> |
| /// <strong>Note</strong>: Although this is implemented for both the |
| /// <a href="./struct.Field.html"><code>Field</code></a> type <em>and</em> any |
| /// type that can be borrowed as an <code>&str</code>, only <code>Field</code> |
| /// allows <em>O</em>(1) access. |
| /// Indexing a field with a string results in an iterative search that performs |
| /// string comparisons. Thus, if possible, once the key for a field is known, it |
| /// should be used whenever possible. |
| /// </pre> |
| </span><span class="kw">pub trait </span>AsField: <span class="kw">crate</span>::sealed::Sealed { |
| <span class="doccomment">/// Attempts to convert `&self` into a `Field` with the specified `metadata`. |
| /// |
| /// If `metadata` defines this field, then the field is returned. Otherwise, |
| /// this returns `None`. |
| </span><span class="kw">fn </span>as_field(<span class="kw-2">&</span><span class="self">self</span>, metadata: <span class="kw-2">&</span>Metadata<<span class="lifetime">'_</span>>) -> <span class="prelude-ty">Option</span><Field>; |
| } |
| |
| <span class="comment">// ===== impl AsField ===== |
| |
| </span><span class="kw">impl </span>AsField <span class="kw">for </span>Field { |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>as_field(<span class="kw-2">&</span><span class="self">self</span>, metadata: <span class="kw-2">&</span>Metadata<<span class="lifetime">'_</span>>) -> <span class="prelude-ty">Option</span><Field> { |
| <span class="kw">if </span><span class="self">self</span>.callsite() == metadata.callsite() { |
| <span class="prelude-val">Some</span>(<span class="self">self</span>.clone()) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> AsField <span class="kw">for </span><span class="kw-2">&</span><span class="lifetime">'a </span>Field { |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>as_field(<span class="kw-2">&</span><span class="self">self</span>, metadata: <span class="kw-2">&</span>Metadata<<span class="lifetime">'_</span>>) -> <span class="prelude-ty">Option</span><Field> { |
| <span class="kw">if </span><span class="self">self</span>.callsite() == metadata.callsite() { |
| <span class="prelude-val">Some</span>((<span class="kw-2">*</span><span class="self">self</span>).clone()) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| } |
| |
| <span class="kw">impl </span>AsField <span class="kw">for </span>str { |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>as_field(<span class="kw-2">&</span><span class="self">self</span>, metadata: <span class="kw-2">&</span>Metadata<<span class="lifetime">'_</span>>) -> <span class="prelude-ty">Option</span><Field> { |
| metadata.fields().field(<span class="kw-2">&</span><span class="self">self</span>) |
| } |
| } |
| |
| <span class="kw">impl </span><span class="kw">crate</span>::sealed::Sealed <span class="kw">for </span>Field {} |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> <span class="kw">crate</span>::sealed::Sealed <span class="kw">for </span><span class="kw-2">&</span><span class="lifetime">'a </span>Field {} |
| <span class="kw">impl </span><span class="kw">crate</span>::sealed::Sealed <span class="kw">for </span>str {} |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="tracing" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
