# io.github.libtmux.query.FilterExpr.not

- **Module:** io.github.libtmux.query.FilterExpr
- **Package:** io.github.libtmux:libtmux-kotlin
- **Language:** Kotlin
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-java/blob/f56392b5d9bc7f1f9c1631842333fb90f3d82d40/libtmux-kotlin/src/main/kotlin/io/github/libtmux/kotlin/Filters.kt#L26
- **Page:** https://libtmux.org/en/kotlin/latest/reference/io-github-libtmux-query-filterexpr-not/

```
public operator fun <T : Any> FilterExpr<T>.not(): FilterExpr<T>
```

Inverts an expression, so `!Pane_.active().isTrue()` says what it means.

There is no matching `and` or `or` here, deliberately. Those are already methods on
[FilterExpr], and an extension of the same name would be shadowed by the member inside its own
body while winning at an infix call site — correct either way, but for a reason no reader should
have to work out. `a.and(b)` is one character longer than `a and b` and always means the thing it
appears to.

`negate` rather than `not` on the Java side because [java.util.function.Predicate] already owns
`not`, and these expressions are predicates.

The bound is `T : Any` rather than `T`, and that is not a style choice. The core is `@NullMarked`,
so Kotlin reads `FilterExpr` as `FilterExpr<T : Any>`; an unbounded `T` here would admit a
nullable entity the core says cannot exist. Compiled with `-Xjspecify-annotations=strict`, so it
is an error rather than a warning — this file did not compile until the bound was written.