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 Subscribers 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§

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impl<'a> Metadata<'a>

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pub const fn new( name: &'static str, target: &'a str, level: Level, file: Option<&'a str>, line: Option<u32>, module_path: Option<&'a str>, fields: FieldSet, kind: Kind ) -> Metadata<'a>

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

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pub fn fields(&self) -> &FieldSet

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

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pub fn level(&self) -> &Level

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

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pub fn name(&self) -> &'static str

Returns the name of the span.

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pub fn target(&self) -> &'a str

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.

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pub fn module_path(&self) -> Option<&'a str>

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

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pub fn file(&self) -> Option<&'a str>

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

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pub fn line(&self) -> Option<u32>

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

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pub fn callsite(&self) -> Identifier

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

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pub fn is_event(&self) -> bool

Returns true if the callsite kind is Event.

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pub fn is_span(&self) -> bool

Return true if the callsite kind is Span.

Trait Implementations§

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impl<'a> AsLog for Metadata<'a>

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type Log = Metadata<'a>

The log type that this type can be converted into.
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fn as_log(&self) -> <Metadata<'a> as AsLog>::Log

Returns the log equivalent of self.
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impl<'a> AsSerde<'a> for Metadata<'a>

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type Serializable = SerializeMetadata<'a>

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fn as_serde(&'a self) -> <Metadata<'a> as AsSerde<'a>>::Serializable

as_serde borrows a tracing value and returns the serialized value.
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impl<'a> Debug for Metadata<'a>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
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impl From<&WasmMetadata> for &'static Metadata<'static>

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fn from(wm: &WasmMetadata) -> &'static Metadata<'static>

Converts to this type from the input type.
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impl<'a> PartialEq<Metadata<'a>> for Metadata<'a>

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fn eq(&self, other: &Metadata<'a>) -> bool

This method tests for self and other values to be equal, and is used by ==.
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fn ne(&self, other: &Rhs) -> bool

This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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impl<'a> Eq for Metadata<'a>

Auto Trait Implementations§

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impl<'a> !RefUnwindSafe for Metadata<'a>

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impl<'a> Send for Metadata<'a>

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impl<'a> Sync for Metadata<'a>

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impl<'a> Unpin for Metadata<'a>

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impl<'a> !UnwindSafe for Metadata<'a>

Blanket Implementations§

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impl<T> Any for Twhere T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
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fn into_any(self: Box<T, Global>) -> Box<dyn Any, Global>

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fn into_any_rc(self: Rc<T>) -> Rc<dyn Any>

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fn type_name(&self) -> &'static str

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Immutably borrows from an owned value. Read more
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Mutably borrows from an owned value. Read more
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Convert from a value of T into an equivalent instance of Option<Self>. Read more
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Converts self into T using Into<T>. Read more
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fn into_any(self: Box<T, Global>) -> Box<dyn Any, Global>

Convert Box<dyn Trait> (where Trait: Downcast) to Box<dyn Any>. Box<dyn Any> can then be further downcast into Box<ConcreteType> where ConcreteType implements Trait.
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Convert Rc<Trait> (where Trait: Downcast) to Rc<Any>. Rc<Any> can then be further downcast into Rc<ConcreteType> where ConcreteType implements Trait.
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Convert &Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &Any’s vtable from &Trait’s.
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Convert &mut Trait (where Trait: Downcast) to &Any. This is needed since Rust cannot generate &mut Any’s vtable from &mut Trait’s.
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fn equivalent(&self, key: &K) -> bool

Compare self to key and return true if they are equal.
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Causes self to use its Binary implementation when Debug-formatted.
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Causes self to use its Display implementation when Debug-formatted.
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Causes self to use its LowerExp implementation when Debug-formatted.
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Causes self to use its LowerHex implementation when Debug-formatted.
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Causes self to use its Octal implementation when Debug-formatted.
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Causes self to use its UpperExp implementation when Debug-formatted.
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Causes self to use its UpperHex implementation when Debug-formatted.
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Instruments this type with the provided Span, returning an Instrumented wrapper. Read more
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Cast reference.
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Pipes by value. This is generally the method you want to use. Read more
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const ALIGN: usize = mem::align_of::<T>()

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