理解“||"Ruby 中 If 条件中的 OR 运算符 [英] Understanding the "||" OR operator in If conditionals in Ruby

问题描述

简单地说，为什么以下三行的影响不同?

Just briefly, why are the following three lines not identical in their impact?

if @controller.controller_name == "projects" || @controller.controller_name == "parts"

if @controller.controller_name == ("projects" || "parts")

if @controller.controller_name == "projects" || "parts"

第一个给出了我想要的结果，但实际上除了项目和零件之外还有更多的选择，使用这种形式会创建一个冗长的语句.其他两个更紧凑，但不要给我相同的结果.

The first gives me the result I want, but as there's actually more options than just projects and parts, using that form creates a verbose statement. The other two are more compact, but don't give me the same result.

推荐答案

|| 的确切语义是:

the exact semantics of || are:

• 如果第一个表达式不是 nil 或 false，则返回它
• 如果第一个表达式为 nil 或 false，则返回第二个表达式

所以你的第一个表达式的结果是，如果 @controller.controller_name == "projects"，那么表达式短路并返回 true.如果没有，它会检查第二个表达式.第二个和第三个变体本质上是 if @controller.controller_name == "projects"，因为 "projects" ||"parts" 等于 "projects".你可以在 irb 中试试这个:

so what your first expression works out to is, if @controller.controller_name == "projects", then the expression short-circuits and returns true. if not, it checks the second expression. the second and third variants are essentially if @controller.controller_name == "projects", since "projects" || "parts" equals "projects". you can try this in irb:

>> "projects" || "parts"
=> "projects"

你想做的是

if ["projects", "parts"].include? @controller.controller_name

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