Ruby on Rails 如何使用 Yield 进行布局？
yield 用于调用区块。在使用 yield 进行布局的 Rails 中，这是如何工作的？
-# application.html.haml
%body= yield
它是否在某处使用块或者该方法只是被覆盖？
yield is used to call a block. How does this work in Rails where yield is used for layouts?
-# application.html.haml
%body= yield
Does it use blocks somewhere or is the method simply overridden?
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从技术上讲，yield 也在这种情况下调用块。但是，该块是您的控制器操作被告知要渲染的视图。
例如，假设您有一个
StaticContentController，其中有一个代表您主页的index操作。正确配置路由后，您将访问您的主页。 Rails 将在适合该控制器的views/layouts中加载布局文件（application.html.haml，除非您使用控制器的布局覆盖它）。当它到达yield命令时，它会将视图插入views/static_content/index.html.haml中yield所在位置。布局。然后，它加载布局文件的其余部分。Technically,
yieldis calling a block in this context as well. However, the block is the view your controller action was told to render.For example, let's say you have a
StaticContentControllerthat has anindexaction on it that represented your home page. With routes configured correctly, you visit your home page. Rails will load the layout file inviews/layoutsthat is appropriate for that controller (application.html.haml, unless you overrode this with a layout for your controller). When it reaches theyieldcommand, it inserts the view atviews/static_content/index.html.hamlat the location whereyieldis inside your layout. Then, it loads the rest of your layout file.默认情况下，所有 Ruby 函数都可以传递一个块：
def twice yield yield end > twice { print 'hi ' } => hi hi考虑布局的最佳方式是使用块调用的方法。
当 Rails 渲染模板时，它实际上是在调用 Layout#render。 Layout#render 接受默认块。默认情况下，Rails 将您的视图作为此块传递。这意味着从布局中调用yield就像调用默认块一样，在本例中是您的视图。
By default all Ruby functions can be passed a block:
def twice yield yield end > twice { print 'hi ' } => hi hiThe best way to think of a layout is a method that is called with a block.
When Rails renders a template, it is actually making a call to Layout#render. Layout#render accepts a default block. By default Rails passes your view as this block. This means that calling yield from within your layout is like calling the default block, which in this case is your view.