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Diffstat (limited to 'guides/source/autoloading_and_reloading_constants.md')
| -rw-r--r-- | guides/source/autoloading_and_reloading_constants.md | 45 |
1 files changed, 29 insertions, 16 deletions
diff --git a/guides/source/autoloading_and_reloading_constants.md b/guides/source/autoloading_and_reloading_constants.md index 489ea681e2..9e78eebf82 100644 --- a/guides/source/autoloading_and_reloading_constants.md +++ b/guides/source/autoloading_and_reloading_constants.md @@ -1,4 +1,4 @@ -**DO NOT READ THIS FILE IN GITHUB, GUIDES ARE PUBLISHED IN http://guides.rubyonrails.org.** +**DO NOT READ THIS FILE ON GITHUB, GUIDES ARE PUBLISHED ON http://guides.rubyonrails.org.** Autoloading and Reloading Constants =================================== @@ -80,7 +80,8 @@ end ``` The *nesting* at any given place is the collection of enclosing nested class and -module objects outwards. For example, in the previous example, the nesting at +module objects outwards. The nesting at any given place can be inspected with +`Module.nesting`. For example, in the previous example, the nesting at (1) is ```ruby @@ -113,6 +114,16 @@ certain nesting does not necessarily correlate with the namespaces at the spot. Even more, they are totally independent, take for instance ```ruby +module X + module Y + end +end + +module A + module B + end +end + module X::Y module A::B # (3) @@ -140,9 +151,10 @@ executed, and popped after it. * A singleton class opened with `class << object` gets pushed, and popped later. -* When any of the `*_eval` family of methods is called using a string argument, +* When `instance_eval` is called using a string argument, the singleton class of the receiver is pushed to the nesting of the eval'ed -code. +code. When `class_eval` or `module_eval` is called using a string argument, +the receiver is pushed to the nesting of the eval'ed code. * The nesting at the top-level of code interpreted by `Kernel#load` is empty unless the `load` call receives a true value as second argument, in which case @@ -153,8 +165,6 @@ the blocks that may be passed to `Class.new` and `Module.new` do not get the class or module being defined pushed to their nesting. That's one of the differences between defining classes and modules in one way or another. -The nesting at any given place can be inspected with `Module.nesting`. - ### Class and Module Definitions are Constant Assignments Let's suppose the following snippet creates a class (rather than reopening it): @@ -236,7 +246,7 @@ end ``` `Post` is not syntax for a class. Rather, `Post` is a regular Ruby constant. If -all is good, the constant evaluates to an object that responds to `all`. +all is good, the constant is evaluated to an object that responds to `all`. That is why we talk about *constant* autoloading, Rails has the ability to load constants on the fly. @@ -291,7 +301,9 @@ order. The ancestors of those elements are ignored. 2. If not found, then the algorithm walks up the ancestor chain of the cref. -3. If not found, `const_missing` is invoked on the cref. The default +3. If not found and the cref is a module, the constant is looked up in `Object`. + +4. If not found, `const_missing` is invoked on the cref. The default implementation of `const_missing` raises `NameError`, but it can be overridden. Rails autoloading **does not emulate this algorithm**, but its starting point is @@ -314,7 +326,7 @@ relative: `::Billing::Invoice`. That would force `Billing` to be looked up only as a top-level constant. `Invoice` on the other hand is qualified by `Billing` and we are going to see -its resolution next. Let's call *parent* to that qualifying class or module +its resolution next. Let's define *parent* to be that qualifying class or module object, that is, `Billing` in the example above. The algorithm for qualified constants goes like this: @@ -330,7 +342,7 @@ checked. Rails autoloading **does not emulate this algorithm**, but its starting point is the name of the constant to be autoloaded, and the parent. See more in -[Qualified References](#qualified-references). +[Qualified References](#autoloading-algorithms-qualified-references). Vocabulary @@ -451,8 +463,9 @@ Also, this collection is configurable via `config.autoload_paths`. For example, by adding this to `config/application.rb`: ```ruby -config.autoload_paths += "#{Rails.root}/lib" +config.autoload_paths << "#{Rails.root}/lib" ``` +`config.autoload_paths` is accessible from environment-specific configuration files, but any changes made to it outside `config/application.rb` don't have an effect. The value of `autoload_paths` can be inspected. In a just generated application it is (edited): @@ -685,12 +698,12 @@ creates an empty module and assigns it to the `Admin` constant on the fly. ### Generic Procedure Relative references are reported to be missing in the cref where they were hit, -and qualified references are reported to be missing in their parent. (See +and qualified references are reported to be missing in their parent (see [Resolution Algorithm for Relative Constants](#resolution-algorithm-for-relative-constants) at the beginning of this guide for the definition of *cref*, and [Resolution Algorithm for Qualified Constants](#resolution-algorithm-for-qualified-constants) for the definition of -*parent*.) +*parent*). The procedure to autoload constant `C` in an arbitrary situation is as follows: @@ -868,8 +881,8 @@ end ``` To resolve `User` Ruby checks `Admin` in the former case, but it does not in -the latter because it does not belong to the nesting. (See [Nesting](#nesting) -and [Resolution Algorithms](#resolution-algorithms).) +the latter because it does not belong to the nesting (see [Nesting](#nesting) +and [Resolution Algorithms](#resolution-algorithms)). Unfortunately Rails autoloading does not know the nesting in the spot where the constant was missing and so it is not able to act as Ruby would. In particular, @@ -1284,7 +1297,7 @@ c.user # NameError: uninitialized constant C::User ``` because it detects that a parent namespace already has the constant (see [Qualified -References](#autoloading-algorithms-qualified-references).) +References](#autoloading-algorithms-qualified-references)). As with pure Ruby, within the body of a direct descendant of `BasicObject` use always absolute constant paths: |