tracing/field.rs
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//! Structured data associated with `Span`s and `Event`s.
pub use tracing_core::field::*;
use crate::Metadata;
/// Trait implemented to allow a type to be used as a field key.
///
/// <div class="example-wrap" style="display:inline-block">
/// <pre class="ignore" style="white-space:normal;font:inherit;">
///
/// **Note**: Although this is implemented for both the [`Field`] type
/// *and* any type that can be borrowed as an `&str`, only `Field` allows *O*(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>
/// </div>
pub trait AsField: crate::sealed::Sealed {
/// 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`.
fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field>;
}
// ===== impl AsField =====
impl AsField for Field {
#[inline]
fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
if self.callsite() == metadata.callsite() {
Some(self.clone())
} else {
None
}
}
}
impl<'a> AsField for &'a Field {
#[inline]
fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
if self.callsite() == metadata.callsite() {
Some((*self).clone())
} else {
None
}
}
}
impl AsField for str {
#[inline]
fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
metadata.fields().field(&self)
}
}
impl crate::sealed::Sealed for Field {}
impl<'a> crate::sealed::Sealed for &'a Field {}
impl crate::sealed::Sealed for str {}