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the same way you would a method with the signature `fun isWeekend(date: Date): Boolean`

That doesn't seem to work, because isn't the isWeekend method in a different scope now?

Let's say my class is as follows:

```
class ExtensionFunctions{
    fun Date.isWeekend() = day == 6 || day == 7
}
```

I won't be able to test it by just calling `isWeekend(Date())` on the class right?

In this case `Date.isWeekend` is both an extension function of `Date` and a member function of `ExtensionFunctions`, so you need both receivers in scope.
In a member-function of `ExtensionFunctions` you can just call `Date().isWeekend()`, outside you would need 
```
with (instanceOfExtensionFunctions) {
    Date().isWeekend()
}
```

All in all I doubt you really wanted to declare the extension function inside a class.

So extension functions can be anywhere? And I will just be able to access them? I think this is the bit of knowledge I am lacking about extension functions... If I were to declarem them in a Kotlin file I should just be able to use them throughout my project? Because this sounds awesome!

Yes, you can make them top-level and they will be available anywhere. Just like normal top-level functions

anywhere in the same file you mean? Not the whole projct right?

Say I had  a Kotlin file called ExtensionFunctions.kt

And its contents were:

```
import java.util.*

fun main(args: Array&lt;String&gt;) {
    fun Date.isWeekend() = day == 6 || day == 7
}
```

That's inside another function, that would be local to the function.

If you put it top-level, it will be available globally

Of course you're right! Yeah... totally works

Thank you for your help! Super appreciate