[swift-evolution] Strings in Swift 4

[Ole Begemann]

> The downside of having two types is the inconvenience of sometimes having
> a
> `Substring` when you need a `String`, and vice-versa. It is likely this
> would
> be a significantly bigger problem than with `Array` and `ArraySlice`, as
> slicing of `String` is such a common operation. It is especially relevant
> to
> existing code that assumes `String` is the currency type.

I'm not familiar with the term "currency type" that appears several
times in the document. Could you clarify what it means? Googling it
proved difficult because all results are about the "money" meaning of
"currency".