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Dependent types are types that depend on values. Scala's match types enable expressing types that depend on types. Scala's other type system features include path-dependent types, which allow types...
#1: Initial revision
by
r~~
·
2026-02-06T03:27:07Z (7 months ago)
Dependent types are types that depend on values. Scala's match types enable expressing types that depend on types. Scala's other type system features include *path*-dependent types, which allow types to depend on paths that represent values, but outside of literals and singletons, there is no way to express values themselves in the type system. So no, these are not full dependent types.
As an example of what isn't possible:
```scala
type MyTuple[n, A] = n match
case 0 => Unit
case 1 => A
case 2 => (A, A)
def myfn(n: Int): MyTuple[n, String] = n match
case 0 => ()
case 1 => ""
case 2 => ("", "")
```
Changing `MyTuple[n, String]` to `MyTuple[n.type, String]` doesn't help. `n.type` is a path-dependent type, so the type system knows that all occurrences of `n.type` are the same, but it doesn't know the run-time value of `n` and so can't reduce `MyTuple` enough to check the three cases.