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kotlinlang

When to use inline functions? I thought, this case would be a nice example for inlining functions, but intellj ide recommendds to remove.
```private inline fun String.isValidFile() = File(this).exists() && File(this).isFile```

there's generally no need to inline functions like that

the jit/optimizer can easily choose to inline it at callsites if it decides it's hot and the space tradeoff is worthwhile

if you explicitly `inline`, then you're always paying the space tradeoff, no choice

higher order functions that take a lambda are much better candidates since inlining reduces allocation and virtual calls, but neither is the case above

Apart from that, `isFile == true` implies `exists() == true`, so just use the former.

I would use the newer `java.nio` features instead of the old `<http://java.io|java.io>` ones:
```private fun String.isValidFile() = Path(this).isRegularFile()```