[swift-evolution] [Discussion] File-level declarations having highest priority for shadowing

Xiaodi Wu xiaodi.wu at gmail.com
Mon Jun 20 13:59:53 CDT 2016

I can see how this is a problem, but I don't like this solution for the
same reasoning that Jordan provided in the bug. Namely, the general rule is
that the inner scope shadows the outer scope. This would be a very strange
exception that you're proposing.

I'd rather cope temporarily with the current limitation, which as you
mentioned has a workaround everywhere except in Playgrounds; in
Playgrounds, there isn't any reason why you couldn't just rename one or the
On Mon, Jun 20, 2016 at 13:55 Charlie Monroe via swift-evolution <
swift-evolution at swift.org> wrote:

> I've filed this previously as a compiler bug, but was told to discuss this
> here (https://bugs.swift.org/browse/SR-1772).
> Motivation:
> Consider the following code:
> private func _validateAccount(name: String, existingAccounts: [Account])
> -> Bool {
>     // Logic goes here...
> }
> class MyController {
>     private func _validateAccount(name: String) -> Bool {
>         let accounts = self.accounts
> // Error: Extra argument 'existingAccounts' in call
>         return _validateAccount(name, existingAccounts: accounts)
>     }
> }
> _validateAccount(name:, existingAccounts:) is declared at file-level since
> it is used in two separate controllers (my example comes from an app with
> accounts and the check is done during creation + when renaming) and then a
> similar method (with less arguments) is declared on the controllers.
> Currently, the compiler gives an error about ambiguous use of
> _validateAccount, since it's declared on MyController as well which is
> taking precedence, even though the number of arguments is different (and
> the compiler is only checking base names, not arguments).
> As Jordan Rose mentioned in a comment to my report, solution to this is to
> specify the function using Module._validateAccount, but this is not
> applicable to Playgrounds.
> This is partially an issue of the ongoing discussion of various name
> collisions between modules, but in this particular case, it's one single
> file.
> I propose that file-level symbols take precedence over any reference to
> current type's members, unless explicit self is specified, or at least when
> it comes to calling a method, the type checker goes up the scope hierarchy
> to see if there isn't a function satisfying the arguments.
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