:this 在 Ruby on Rails 中是什么意思? [英] What does :this means in Ruby on Rails?

问题描述

我是 Ruby 和 Ruby on Rails 世界的新手.我已经阅读了一些指南，但我在使用以下语法时遇到了一些麻烦.我认为在 Ruby 中使用 :condition 语法来定义具有某种访问器的类属性，例如:

I'm new to the Ruby and Ruby on Rails world. I've read some guides, but i've some trouble with the following syntax. I think that the usage of :condition syntax is used in Ruby to define a class attribute with some kind of accessor, like:

class Sample
  attr_accessor :condition
end

隐式声明了条件"属性的 getter 和 setter.当我查看一些 Rails 示例代码时，我发现以下示例我并不完全理解.

that implicitly declares the getter and setter for the "condition" property. While i was looking at some Rails sample code, i found the following examples that i don't fully understand.

例如:

@post = Post.find(params[:id])

为什么它使用这种语法访问 id 属性，而不是:

Why it's accessing the id attribute with this syntax, instead of:

@post = Post.find(params[id])

或者，例如:

Or, for example:

@posts = Post.find(:all) 

:all 是一个常量吗?如果不是，这段代码的真正含义是什么?如果是，为什么不使用以下内容:

Is :all a constant here? If not, what does this code really means? If yes, why the following is not used:

@posts = Post.find(ALL)

谢谢

推荐答案

文本前的冒号表示 Ruby 中的符号.一个符号有点像一个常量，但它几乎就像一个符号接收一个唯一的值(你不关心)作为它的常量值.

A colon before text indicates a symbol in Ruby. A symbol is kind of like a constant, but it's almost as though a symbol receives a unique value (that you don't care about) as its constant value.

当用作哈希索引时，符号几乎(但不完全)与使用字符串相同.

When used as a hash index, symbols are almost (but not exactly) the same as using strings.

此外，您可以通过在符号上调用 to_s 从 :all 读取all".如果您有一个常量变量 ALL，除了查找它的值之外，没有办法确定它的意思是所有".这也是为什么您可以使用符号作为元方法的参数，例如 attr_accessor、attr_reader 等.

Also, you can read "all" from :all by calling to_s on the symbol. If you had a constant variable ALL, there would be no way to determine that it meant "all" other than looking up its value. This is also why you can use symbols as arguments to meta-methods like attr_accessor, attr_reader, and the like.

您可能想要阅读 Ruby 符号.

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