Module tracing::field

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Structured data associated with Spans and Events.


  • A Value which serializes as a string using fmt::Debug.
  • A Value which serializes using fmt::Display.
  • An empty field.
  • An opaque key allowing O(1) access to a field in a Span’s key-value data.
  • Describes the fields present on a span.
  • An iterator over a set of fields.
  • A set of fields and values for a span.


  • Trait implemented to allow a type to be used as a field key.
  • A field value of an erased type.
  • Visits typed values.


  • Wraps a type implementing fmt::Debug as a Value that can be recorded using its Debug implementation.
  • Wraps a type implementing fmt::Display as a Value that can be recorded using its Display implementation.