🛈 Note: This is pre-release documentation for the upcoming tracing 0.2.0 ecosystem.

For the release documentation, please see docs.rs, instead.

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pub struct Metadata<'a> { /* private fields */ }
Expand description

Metadata describing a span or event.

All spans and events have the following metadata:

  • A name, represented as a static string.
  • A target, a string that categorizes part of the system where the span or event occurred. The tracing macros default to using the module path where the span or event originated as the target, but it may be overridden.
  • A verbosity level. This determines how verbose a given span or event is, and allows enabling or disabling more verbose diagnostics situationally. See the documentation for the Level type for details.
  • The names of the fields defined by the span or event.
  • Whether the metadata corresponds to a span or event.

In addition, the following optional metadata describing the source code location where the span or event originated may be provided:

Metadata is used by collectors when filtering spans and events, and it may also be used as part of their data payload.

When created by the event! or span! macro, the metadata describing a particular event or span is constructed statically and exists as a single static instance. Thus, the overhead of creating the metadata is significantly lower than that of creating the actual span. Therefore, filtering is based on metadata, rather than on the constructed span.

Equality

In well-behaved applications, two Metadata with equal callsite identifiers will be equal in all other ways (i.e., have the same name, target, etc.). Consequently, in release builds, Metadata::eq only checks that its arguments have equal callsites. However, the equality of Metadata’s other fields is checked in debug builds.

Implementations

Construct new metadata for a span or event, with a name, target, level, field names, and optional source code location.

Returns the names of the fields on the described span or event.

Returns the level of verbosity of the described span or event.

Returns the name of the span.

Returns a string describing the part of the system where the span or event that this metadata describes occurred.

Typically, this is the module path, but alternate targets may be set when spans or events are constructed.

Returns the path to the Rust module where the span occurred, or None if the module path is unknown.

Returns the name of the source code file where the span occurred, or None if the file is unknown

Returns the line number in the source code file where the span occurred, or None if the line number is unknown.

Returns an opaque Identifier that uniquely identifies the callsite this Metadata originated from.

Returns true if the callsite kind is Event.

Return true if the callsite kind is Span.

Trait Implementations

Formats the value using the given formatter. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Instruments this type with the provided Span, returning an Instrumented wrapper. Read more

Instruments this type with the current Span, returning an Instrumented wrapper. Read more

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.

Available on crate feature std only.

Attaches the provided collector to this type, returning a WithDispatch wrapper. Read more

Available on crate feature std only.

Attaches the current default collector to this type, returning a WithDispatch wrapper. Read more