Module predicates

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Predicates for CapturedSpans and CapturedEvents.

§Overview

A predicate can be created with the functions from this module:

level() checks the span / event level
name() checks the span name
target() checks the span / event target
field() checks a specific span / event field
message() checks the event message
parent() checks the direct parent span of an event / span
ancestor() checks the ancestor spans of an event / span

These predicates can be combined with bitwise operators, & and |. The ScanExt trait may be used to simplify assertions with predicates. The remaining traits and structs are lower-level plumbing and rarely need to be used directly.

§Examples

// Predicates can be combined using bitwise operators:
let predicate = target([eq("tracing")])
    & name(eq("test_capture"))
    & level(Level::INFO)
    & field("result", 42_i64);
// The resulting predicate can be used with `CapturedExt` trait.
let storage: &Storage = // ...
let _ = storage.scan_spans().first(&predicate);
let _ = storage.scan_events().single(&level(Level::ERROR));

// ...or converted back to a closure:
let _ = storage.all_spans().filter(into_fn(predicate));

Structs§

AncestorPredicate: Predicate for the ancestors of a CapturedSpan or CapturedEvent returned by the ancestor() function.
And: Boolean “and” combinator for predicates. Produced by the bitwise and (&) operator on the base predicates from this module.
FieldPredicate: Predicate for a particular field of a CapturedSpan or CapturedEvent returned by the field() function.
LevelPredicate: Predicate for the Level of a CapturedSpan or CapturedEvent returned by the level() function.
MessagePredicate: Predicate for the message of a CapturedEvent returned by the message() function.
NamePredicate: Predicate for the name of a CapturedSpan returned by the name() function.
Or: Boolean “or” combinator for predicates. Produced by the bitwise or (|) operator on the base predicates from this module.
ParentPredicate: Predicate for the parent of a CapturedSpan or CapturedEvent returned by the parent() function.
Scanner: Helper that allows using Predicates rather than closures to find matching elements, and provides more informative error messages.
TargetPredicate: Predicate for the target of a CapturedSpan or CapturedEvent returned by the target() function.
ValuePredicate: Predicate for TracedValues returned by the value() function.

Traits§

IntoFieldPredicate: Conversion into a predicate for a TracedValue used in the field() function.
IntoLevelPredicate: Conversion into a predicate for Levels used in the level() function.
IntoTargetPredicate: Conversion into a predicate for the target used in the target() function.
ScanExt: Helper to wrap holders of CapturedSpans or CapturedEvents (spans or the underlying Storage) so that they are more convenient to use with Predicates.

Functions§

ancestor: Creates a predicate for ancestor CapturedSpans of a span or a CapturedEvent. The predicate is true iff the wrapped span predicate holds true for any of the ancestors.
field: Creates a predicate for a particular field of a CapturedSpan or CapturedEvent.
into_fn: Converts a predicate into an Fn(_) -> bool closure.
level: Creates a predicate for the Level of a CapturedSpan or CapturedEvent.
message: Creates a predicate for the message of a CapturedEvent.
name: Creates a predicate for the name of a CapturedSpan.
parent: Creates a predicate for the direct parent CapturedSpan of a span or a CapturedEvent.
target: Creates a predicate for the target of a CapturedSpan or CapturedEvent.
value: Creates a predicate for a TracedValue that checks whether the value matches the specified criteria for a particular subtype (e.g., an unsigned integer). If the value has another subtype, the predicate is false.