[Wildcard Variables][spec] `_` in imports

[kallentu]

Do we allow an import statement like import ... as _;? And if so, what does this do? Is this also non-binding?

@dart-lang/language-team

Previous Discussion

Maybe we should make _ non-binding as an import prefix?

It's like a top-level declaration, but it's also only available in the lexical scope. If you want to import a library only for it's extensions, you may want to import it with a prefix, and never need to refer to it, and as _ would work for that.

Originally posted by @lrhn in #3791

[eernstg]

Make it non-binding such that it can be used to provide access to just the extensions (and possibly other declarations that get a similar treatment, e.g., implicit constructors).

This would make it possible to use import 'a.dart' as _; import 'b.dart' as _; etc. to import a bunch of extensions (and "similar things", if any, but nothing else). We wouldn't have to think about the appropriateness of using _ all over the place as an import prefix (because it doesn't work), and the developer wouldn't have to avoid name clashes among all those _.

Sounds like an OK job for a wildcard.

[kallentu]

Great. Adding a section on the spec. #3819