1 //! Structured data associated with `Span`s and `Event`s.
2 pub use tracing_core::field::*;
3 
4 use crate::Metadata;
5 
6 /// Trait implemented to allow a type to be used as a field key.
7 ///
8 /// <div class="information">
9 ///     <div class="tooltip ignore" style="">ⓘ<span class="tooltiptext">Note</span></div>
10 /// </div>
11 /// <div class="example-wrap" style="display:inline-block">
12 /// <pre class="ignore" style="white-space:normal;font:inherit;">
13 /// <strong>Note</strong>: Although this is implemented for both the
14 /// <a href="./struct.Field.html"><code>Field</code></a> type <em>and</em> any
15 /// type that can be borrowed as an <code>&str</code>, only <code>Field</code>
16 /// allows <em>O</em>(1) access.
17 /// Indexing a field with a string results in an iterative search that performs
18 /// string comparisons. Thus, if possible, once the key for a field is known, it
19 /// should be used whenever possible.
20 /// </pre>
21 pub trait AsField: crate::sealed::Sealed {
22     /// Attempts to convert `&self` into a `Field` with the specified `metadata`.
23     ///
24     /// If `metadata` defines this field, then the field is returned. Otherwise,
25     /// this returns `None`.
as_field(&self, metadata: &Metadata<'_>) -> Option<Field>26     fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field>;
27 }
28 
29 // ===== impl AsField =====
30 
31 impl AsField for Field {
32     #[inline]
as_field(&self, metadata: &Metadata<'_>) -> Option<Field>33     fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
34         if self.callsite() == metadata.callsite() {
35             Some(self.clone())
36         } else {
37             None
38         }
39     }
40 }
41 
42 impl<'a> AsField for &'a Field {
43     #[inline]
as_field(&self, metadata: &Metadata<'_>) -> Option<Field>44     fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
45         if self.callsite() == metadata.callsite() {
46             Some((*self).clone())
47         } else {
48             None
49         }
50     }
51 }
52 
53 impl AsField for str {
54     #[inline]
as_field(&self, metadata: &Metadata<'_>) -> Option<Field>55     fn as_field(&self, metadata: &Metadata<'_>) -> Option<Field> {
56         metadata.fields().field(&self)
57     }
58 }
59 
60 impl crate::sealed::Sealed for Field {}
61 impl<'a> crate::sealed::Sealed for &'a Field {}
62 impl crate::sealed::Sealed for str {}
63