问号和冒号 - 如果在 ruby 中
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question mark and colon - if else in ruby
提问by u19964
Hi I have a question about ruby on rails
嗨，我有一个关于 ruby on rails 的问题
Apparently I have a statement like this:
显然我有这样的声明：
def sort_column
Product.column_names.include?(params[:sort]) ? params[:sort] : "name"
end
From what I read, it's said that this method sort the column based on params[:sort] and if there no params the products will be sorted by "name". However, I don't understand the way this statement is written, especially the second "?". Can someone explain it to me ?
从我读到的内容来看，据说此方法根据 params[:sort] 对列进行排序，如果没有 params，则产品将按“名称”排序。但是，我不明白这个语句的写法，尤其是第二个“？”。有人可以向我解释一下吗？
回答by Sergio Tulentsev
This is your code, rearranged for easier understanding.
这是您的代码，为了更容易理解而重新排列。
def sort_column
cond = Product.column_names.include?(params[:sort])
cond ? params[:sort] : "name"
# it's equivalent to this
# if cond
# params[:sort]
# else
# 'name'
# end
end
First question mark is part of a method name, the second one - part of ternary operator (which you should read about).
第一个问号是方法名称的一部分，第二个 - 三元运算符的一部分（您应该阅读）。
回答by Matheus Moreira
?:is a ternary operatorthat is present in many languages. It has the following syntax:
expression ? value_if_true : value_if_false
In Ruby, it is a shorter version of this:
在 Ruby 中，它是一个较短的版本：
if expression
value_if_true
else
value_if_false
end
回答by LanceH
That line translates roughly as:
该行大致翻译为：
if Product.column_names.include?(params[:sort])
params[:sort]
else
"name"
end
The ? : is a ternary operator; shorthand for a brief if-else.
这 ？: 是一个三元运算符；简短的 if-else 的简写。
回答by André Medeiros
Product.column_names.include?(params[:sort]) ? params[:sort] : "name"
The first question mark is part of the method name: include?.
第一个问号是方法名称的一部分：include?。
The second question mark and the colon are part of the ternary operand:
(if this is true) ? (do this) : (else, do that).
第二个问号和冒号是三元操作数的一部分：
(if this is true) ? (do this) : (else, do that).
It means that, if Product.column_namescontains params[:sort], it will return params[:sort]. Else, it will return "name".
这意味着，如果Product.column_names包含params[:sort]，它将返回params[:sort]。否则，它将返回"name"。
回答by Cris R
We must to be careful with the expression part to be evaluated in the ternary operator, for instance when using andversus &&, this is what could happen:
我们必须小心在三元运算符中要计算的表达式部分，例如在使用andvs 时&&，可能会发生以下情况：
2.6.2 :014 > a = false
=> false
2.6.2 :015 > b = true
=> true
2.6.2 :016 > a and b ? 'first' : 'second'
=> false
2.6.2 :017 > a && b ? 'first' : 'second'
=> "second"
2.6.2 :018 > (a and b) ? 'first' : 'second'
=> "second"
