Update extension methods specification for prefix imports. #672
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Allow extensions imported with a prefix to be accessible for implicit invocation, but make them less specific than any extension imported without a prefix.
This was referenced Nov 11, 2019
leafpetersen
approved these changes
Nov 12, 2019
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| Implicit extension member invocation can also apply to individual *cascade* invocations. A cascade is treated as if each cascade section was a separate member invocation on an expression with the same value as the cascade receiver expression (the expression before the first `..`). This means that a cascade like `o..foo()..bar()` may perform an implicit extension member invocation on `o` for `foo()` and a normal invocation on `o` for `bar()`. There is no way to specify the corresponding explicit member invocation without expanding the cascade to a sequence of individual member invocations. | ||
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| ##### Accessibility | ||
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| An extension is *accessible* for an expression if it is declared in the current library, or if there is a non-deferred `import` declaration in the current library of a library with the extension in its export scope, where the name of the extension is not private and it is not hidden by a `hide` or `show` modifier of the import. _This includes (non-deferred) imports with a prefix._ | ||
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| It is a *compile-time error* if a deferred import declaration imports a library with an extension declaration in its export scope, unless all such extensions are hidden by `show` or `hide` modifiers on the deferred import. *This is a temporary restriction ensuring that no extensions are introduced using deferred imports, and it allows us to later introduce any semantics for such extensions without affecting existing code*. |
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hide only. show is an error as well.
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Ah, I understand, you mean that the extension is hidden by a show of something else. I found this confusing though. Consider re-phrasing?
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Or will do, I actually updated the paragraph below instead.
| 3. *T<sub>1</sub>* is a subtype of of *T<sub>2</sub>* and either | ||
| 4. not vice versa, or | ||
| 5. the instantiate-to-bounds `on` type of `E1` is a subtype of the instantiate-to-bounds `on` type of `E2` and not vice versa. | ||
| 1. The `E2` extension is only accessible from imports with a prefix and `E1` not, or |
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Allow extensions imported with a prefix to be accessible for implicit invocation, but make them less specific than any extension imported without a prefix.