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Nanaloveyuki
77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
---
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name: not
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group: api
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category: filtering
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update-time: 20260512
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description: Create a reusable record predicate that negates another predicate.
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key-word:
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- negate
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- filter
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- predicate
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- public
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---
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## Not
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Create a `RecordPredicate` that returns the logical inverse of another predicate. This helper is the standard way to express exclusion rules without rewriting predicate bodies.
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### Interface
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```moonbit
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pub fn not_(predicate : RecordPredicate) -> RecordPredicate {}
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```
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#### input
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- `predicate : RecordPredicate` - Existing predicate to invert.
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#### output
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- `RecordPredicate` - Predicate that returns `true` when the original predicate returns `false`.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- `not_(...)` delegates evaluation to the original predicate and flips the boolean result.
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- It does not change the record or short-circuit upstream logic outside the wrapped predicate.
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- This helper is useful for excluding known noisy targets, fields, or message patterns.
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- It composes well with `all_of(...)` and `any_of(...)` for more expressive routing rules.
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### How to Use
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Here are some specific examples provided.
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#### When Exclude One Target Prefix
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When everything except one noisy subsystem should pass:
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```moonbit
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let logger = Logger::new(console_sink())
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.with_filter(not_(target_has_prefix("debug.spam")))
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```
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In this example, records under `debug.spam...` are filtered out.
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#### When Invert A Field Match
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When one tenant should be excluded from a shared stream:
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```moonbit
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let predicate = not_(field_equals("tenant", "internal"))
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```
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In this example, all non-internal tenant records continue through the filter.
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### Error Case
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e.g.:
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- If the wrapped predicate always returns `true`, the negated predicate always returns `false`.
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- If the wrapped predicate is too broad, the inversion may unintentionally admit unrelated records.
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### Notes
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1. Prefer `not_(...)` over duplicating inverse logic inline because the intent is easier to read.
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2. Negation is most maintainable when the wrapped predicate is itself narrow and well named.
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