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| -rw-r--r-- | guides/source/constant_autoloading_and_reloading.md | 55 |
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diff --git a/guides/source/constant_autoloading_and_reloading.md b/guides/source/constant_autoloading_and_reloading.md index c552f2bfa3..aba87cc01c 100644 --- a/guides/source/constant_autoloading_and_reloading.md +++ b/guides/source/constant_autoloading_and_reloading.md @@ -1062,6 +1062,8 @@ spots. ### When Constants aren't Missed +#### Relative References + Let's consider a flight simulator. The application has a default flight model ```ruby @@ -1122,6 +1124,59 @@ module BellX1 end ``` +#### Qualified References + +Given + +```ruby +# app/models/hotel.rb +class Hotel +end + +# app/models/image.rb +class Image +end + +# app/models/hotel/image.rb +class Hotel + class Image < Image + end +end +``` + +the expression `Hotel::Image` is ambiguous, depends on the execution path. + +As [we saw before](#resolution-algorithm-for-qualified-constants), Ruby looks +up the constant in `Hotel` and its ancestors. If `app/models/image.rb` has +been loaded but `app/models/hotel/image.rb` hasn't, Ruby does not find `Image` +in `Hotel`, but it does in `Object`: + +``` +$ bin/rails r 'Image; p Hotel::Image' 2>/dev/null +Image # NOT Hotel::Image! +``` + +The code evaluating `Hotel::Image` needs to make sure +`app/models/hotel/image.rb` has been loaded, possibly with +`require_dependency`. + +In these cases the interpreter issues a warning though: + +``` +warning: toplevel constant Image referenced by Hotel::Image +``` + +This surprising constant resolution can be observed with any qualifying class: + +``` +2.1.5 :001 > String::Array +(irb):1: warning: toplevel constant Array referenced by String::Array + => Array +``` + +WARNING. To find this gotcha the qualifying namespace has to be a class, +`Object` is not an ancestor of modules. + ### Autoloading within Singleton Classes Let's suppose we have these class definitions: |