Android has five storage models, and your path strings only work in one of them

The seam worth arguing about is the single place the two access chains agree: both of them end in a stream ^[4]. Before that, one has a path that becomes a `File`, and the other has a URI that becomes a `ContentResolver` or `DocumentsContract` call into a provider ^[3][4]. That fixes the limit of what a cross-platform storage layer can honestly promise. Handing back an `InputStream` travels ^[14]. Doing arithmetic on names does not ^[7].

The worked example in the post is worth counting. A library whose API takes `documents/example.txt` gets that for free on the JVM, where the string is a path to something on a filesystem ^[7]. Under a user-selected SAF tree, the same string has to be walked: the selected root, then `Documents`, then `projects`, then the file ^[9], and each step is a document-provider operation rather than a traversal of a mounted filesystem ^[8]. Three segments below the root, three provider operations ^[10]. The string also carries no handle to any of the intermediate documents ^[7], so anything resembling a working directory, or a cache of resolved parents, is something the library has to invent rather than something the platform hands over.

The indirection that makes this expensive is the same indirection the author praises. A granted document tree may be backed by a provider that is not local device storage at all, possibly remote or cloud-backed, and the application does not need to know which ^[6]. The post calls that one of the most powerful ideas behind SAF ^[6], and in the next breath warns that an abstraction which tries to hide every difference can be made worse by the hiding ^[12]. Those two positions are compatible only if the leak is deliberate: the layer resolves, opens and streams, and refuses to pretend it can tell you a parent path.

Which is why the count of five is a ceiling rather than a requirement. The post's own routing is narrow: application data belongs in application-private storage, supported shared media belongs in MediaStore, and SAF earns its keep when the requirement is specifically that a user picks a directory and the application then works inside it ^[5]. Strip that requirement and two models cover the app, not five ^[13]. Scoped storage is described as having made storage simpler for many applications for exactly this reason, since private directories plus the appropriate platform APIs remove the need for unrestricted access to the user's shared filesystem ^[11].

The cost, then, sits in an application's internal vocabulary rather than in any API surface. Code that passes `String` paths between its own modules has already decided it is running on a filesystem. This is one practitioner's account of building such a library [c2b], not a platform announcement, and the supplied text breaks off mid-sentence on the question of how much difference an abstraction should hide ^[12].