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Merged
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Mar 13, 2021
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reduced number of Logarithm #11677

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991ea62
reduced number of Logarithm
xhudik Mar 9, 2021
4b77a19
fixed: Logarithms->MyMaths in text
xhudik Mar 12, 2021
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10 changes: 5 additions & 5 deletions docs/docs/reference/other-new-features/opaques.md
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Expand Up @@ -6,7 +6,7 @@ title: "Opaque Type Aliases"
Opaque types aliases provide type abstraction without any overhead. Example:

```scala
object Logarithms:
object MyMath:

opaque type Logarithm = Double

Expand All @@ -27,21 +27,21 @@ object Logarithms:
def + (y: Logarithm): Logarithm = Logarithm(math.exp(x) + math.exp(y))
def * (y: Logarithm): Logarithm = x + y

end Logarithms
end MyMath
```

This introduces `Logarithm` as a new abstract type, which is implemented as `Double`.
The fact that `Logarithm` is the same as `Double` is only known in the scope where
`Logarithm` is defined which in the above example corresponds to the object `Logarithms`.
`Logarithm` is defined which in the above example corresponds to the object `MyMath`.
Or in other words, within the scope it is treated as type alias, but this is opaque to the outside world
where in consequence `Logarithm` is seen as an abstract type and has nothing to do with `Double`.

The public API of `Logarithm` consists of the `apply` and `safe` methods defined in the companion object.
They convert from `Double`s to `Logarithm` values. Moreover, an operation `toDouble` that converts the other way, and operations `+` and `*` are defined as extension methods on `Logarithm` values.
The following operations would be valid because they use functionality implemented in the `Logarithms` object.
The following operations would be valid because they use functionality implemented in the `MyMath` object.

```scala
import Logarithms.Logarithm
import MyMath.Logarithm

val l = Logarithm(1.0)
val l2 = Logarithm(2.0)
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