理解“||”在Ruby中的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相同？

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"

第一部分给出了我想要的结果，但实际上有更多选项而不仅仅是项目和部分，使用该表单创建一个详细的语句。另外两个更紧凑，但不会给我相同的结果。

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：

• 如果第一个表达式不是nil或false，则返回


• 如果第一个表达式是nil或false，返回第二个表达式

所以你的第一个表达式是，如果 @controller .controller_name ==projects，然后表达式短路并返回 true 。如果没有，它会检查第二个表达式。第二个和第三个变体基本上是，如果@ 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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