<%= ... %> 和有什么区别?和<%...%>在 Ruby on Rails 中 [英] What is the difference between <%= ... %> and <% ... %> in Ruby on Rails

问题描述

和输出有关系吗?

所以，<%= ...code... %> 用于代码执行后的输出，<% ...code... %> 只用于执行代码?

So, <%= ...code... %> is used for outputting after code is executed, and <% ...code... %> is only used for executing the code?

推荐答案

这是ERB 模板标记(Rails 支持的众多模板语言之一).此标记:

This is ERB templating markup (one of many templating languages supported by Rails). This markup:

<% ... %>

用于评估 Ruby 表达式.但是，该表达式的结果没有任何处理.相比之下，标记:

is used to evaluate a Ruby expression. Nothing is done with the result of that expression, however. By contrast, the markup:

<%= ... %>

做同样的事情(运行里面的任何 Ruby 代码)但它对结果调用 to_s 并用结果字符串替换标记.

does the same thing (runs whatever Ruby code is inside there) but it calls to_s on the result and replaces the markup with the resulting string.

简而言之:

<% just run code %>
<%= run code and output the result %>

例如:

<% unless @items.empty? %>
  <ul>
    <% @items.each do |item| %>
      <li><%= item.name %></li>
    <% end %>
  </ul> 
<% end %>

相比之下，这里有一些与上面等效的 Haml 标记:

- unless @items.empty?
  %ul
    - @items.each do |item|
      %li= item.name

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