环境/*.rb中的配置符号是如何解析的 [英] How is the config symbol resolved in environments/*.rb

问题描述

典型的 config/environments/*.rb 文件是这样开始的:

This is how a typical config/environments/*.rb file begins:

MyApp::Application.configure do
  config.cache_classes = false
  ...
end

传递给 configure 的块取消引用了显然未绑定的符号 config.这在技术上是如何工作的?块/Proc/lambda 中使用的符号应该在其声明的上下文中绑定，而不是留在调用站点的动态范围内解析.

The block passed to configure dereferences the symbol config which is apparently unbound. How does this technically work? The symbols used in a block/Proc/lambda should be bound in the context of its declaration, not left to be resolved in the dynamic scope at the call site.

一个相关的问题是，Application.configure 方法究竟在哪里声明?它不在 application.rb 中, engine.rb 或 railtie.rb.也许如果我设法找到了这个方法，我就会找到我主要问题的答案.

A related question is, where exactly is the Application.configure method declared? It's not in either application.rb, engine.rb, or railtie.rb. Maybe if I managed to find this method, I would have found the answer to my main question.

同样相关，我研究了Rails 初始化过程 非常详细，我什至找不到提及config/environments/*.rb 文件.如果我知道 init 过程如何处理这些文件，那可能会对此有所了解.

Also related, I have studied the Rails initialization procedure in excruciating detail, and I can't find even a mention of a config/environments/*.rb file. If I knew how these files were treated by the init procedure, that may shed some light on this.

推荐答案

It's a method config in Rails::Application in the railties gem in lib/rails/application.rb 返回一个 Application::Configuration 的实例，在 lib/rails/application/configuration.rb 中定义.

It's a method config in Rails::Application in the railties gem in lib/rails/application.rb which returns an instance of Application::Configuration, defined in lib/rails/application/configuration.rb.

方法 configure 是从 autoloaded 模块 Configurable、lib/贡献给 Railtierails/railtie/configurable，定义为

The method configure is contributed to Railtie from the autoloaded module Configurable, lib/rails/railtie/configurable, and is defined as

def configure(&block)
  class_eval(&block)
end

这解释了为什么 configure 接受的块可以解析 config 符号.请注意，class_eval 是 ruby​​ist 的另一个魔法，它使这项工作成功:它将传入块的 self 符号重新绑定到调用站点的类.

which explains why the block that configure accepts can resolve the config symbol. Note that class_eval is another piece of rubyist magic that makes this work: it rebinds the passed-in block's self symbol to the call site's class.

检查启动过程部分第一个文件中的注释，其中解释了所有这些优点的来源、方式和顺序，包括如何处理 /config/environments 目录.

Check the comments in the first file in the Booting Process section, which explains where, how and in what order all this goodness comes from, including how the /config/environments directory is processed.

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