Struct tracing_core::Metadata
source · [−]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:
- The file name
- The line number
- The module path
Metadata is used by Subscriber
s 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.
Note: Although instances ofMetadata
cannot be compared directly, they provide a methodid
, returning an opaque callsite identifierwhich uniquely identifies the callsite where the metadata originated. This can be used to determine if twoMetadata
correspond to the same callsite.
Implementations
sourceimpl<'a> Metadata<'a>
impl<'a> Metadata<'a>
sourcepub 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
) -> Self
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
) -> Self
Construct new metadata for a span or event, with a name, target, level, field names, and optional source code location.
sourcepub fn fields(&self) -> &FieldSet
pub fn fields(&self) -> &FieldSet
Returns the names of the fields on the described span or event.
sourcepub fn target(&self) -> &'a str
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.
sourcepub fn module_path(&self) -> Option<&'a str>
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.
sourcepub fn file(&self) -> Option<&'a str>
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
sourcepub fn line(&self) -> Option<u32>
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.
sourcepub fn callsite(&self) -> Identifier
pub fn callsite(&self) -> Identifier
Returns an opaque Identifier
that uniquely identifies the callsite
this Metadata
originated from.
Trait Implementations
Auto Trait Implementations
impl<'a> !RefUnwindSafe for Metadata<'a>
impl<'a> Send for Metadata<'a>
impl<'a> Sync for Metadata<'a>
impl<'a> Unpin for Metadata<'a>
impl<'a> !UnwindSafe for Metadata<'a>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for T where
T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
const: unstable · sourcepub fn borrow_mut(&mut self) -> &mut T
pub fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more