Module tracing_core::field [−][src]
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.
Values and Subscribers
Subscribers consume Values as fields attached to spans or Events.
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 Records 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, bool, and &str) or using a fmt::Display or fmt::Debug
implementation. Subscribers 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,
we might record integers by incrementing counters for their field names,
rather than printing them.
Structs
| DebugValue | A |
| DisplayValue | A |
| Empty | An empty field. |
| Field | An opaque key allowing O(1) access to a field in a |
| FieldSet | Describes the fields present on a span. |
| Iter | An iterator over a set of fields. |
| ValueSet | A set of fields and values for a span. |
Traits
| Value | A field value of an erased type. |
| Visit | Visits typed values. |
Functions
| debug | Wraps a type implementing |
| display | Wraps a type implementing |