如何在Ruby中使用条件运算符（？:)？ [英] How do I use the conditional operator (? :) in Ruby?

问题描述

在Ruby中如何使用条件运算符（？：）？

How is the conditional operator (? :) used in Ruby?

例如，这是正确的吗？ ？

For example, is this correct?

<% question = question.size > 20 ? question.question.slice(0, 20)+"..." : question.question %>

推荐答案

它是三元运算符，其工作方式类似于C语言（不需要括号）。该表达式的工作方式如下：

It is the ternary operator, and it works like in C (the parenthesis are not required). It's an expression that works like:

if_this_is_a_true_value ? then_the_result_is_this : else_it_is_this

但是，在Ruby中，如果 >也是一个表达式，因此：如果a然后b else c end === a？ b：c ，优先级问题除外。

However, in Ruby, if is also an expression so: if a then b else c end === a ? b : c, except for precedence issues. Both are expressions.

示例：

puts (if 1 then 2 else 3 end) # => 2

puts 1 ? 2 : 3                # => 2

x = if 1 then 2 else 3 end
puts x                        # => 2

请注意，在第一种情况下，必须使用括号（否则Ruby会感到困惑，因为它认为放入1 ，然后加上一些垃圾），但在最后一种情况下则不需要，因为不会出现上述问题。

Note that in the first case parenthesis are required (otherwise Ruby is confused because it thinks it is puts if 1 with some extra junk after it), but they are not required in the last case as said issue does not arise.

您可以在多行中使用 long-if格式以提高可读性：

You can use the "long-if" form for readability on multiple lines:

question = if question.size > 20 then
  question.slice(0, 20) + "..."
else 
  question
end

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