Module predicates

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 [Level]s 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.