# io.github.libtmux.scaladsl.query.IterableOnce.exactlyOne

- **Module:** io.github.libtmux.scaladsl.query.IterableOnce
- **Package:** io.github.libtmux:libtmux-scala_3
- **Language:** Scala
- **Kind:** function
- **Source:** https://github.com/libtmux/libtmux-java/blob/f56392b5d9bc7f1f9c1631842333fb90f3d82d40/libtmux-scala/src/main/scala/io/github/libtmux/scaladsl/query/CardinalityError.scala#L31
- **Page:** https://libtmux.org/en/scala/latest/reference/io-github-libtmux-scaladsl-query-iterableonce-exactlyone/

```
extension [A](values: IterableOnce[A])
def exactlyOne: Either[CardinalityError, A]
```

The single match, or a failure naming which way the count was wrong. Single-pass: mirrors `Selections.exactlyOne`'s early exit, stopping at the second match.