什么？红宝石的意思[重复]

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How do I use the conditional operator (? :) in Ruby? 6 answers

如何在Ruby中使用条件运算符(?:)? 6个答案

What does the line below checks and perform?

下面的行检查和执行什么?

prefix = root_dir.nil? ? nil : File.join(root_dir, '/')

Here is the block that contains the line of code.

这是包含代码行的块。

def some_name(root_dir = nil, environment = 'stage', branch)
        prefix = root_dir.nil? ? nil : File.join(root_dir, '/')
.
.
.

i know that the '?' in ruby is something that checks the yes/no fulfillment. But I am not very clear on its usage/syntax in the above block of code.

我知道'?'在红宝石中是检查是/否履行的东西。但我对上面的代码块中的用法/语法不是很清楚。

3 个解决方案

#1

Functions that end with ? in Ruby are functions that only return a boolean, that is, true, or false.

最终的功能? Ruby中的函数只返回一个布尔值,即true或false。

When you write a function that can only return true or false, you should end the function name with a question mark.

当您编写只能返回true或false的函数时,您应该使用问号结束函数名称。

The example you gave shows a ternary statement, which is a one-line if-statement. .nil? is a boolean function that returns true if the value is nil and false if it is not. It first checks if the function is true, or false. Then performs an if/else to assign the value (if the .nil? function returns true, it gets nil as value, else it gets the File.join(root_dir, '/') as value.

您给出的示例显示了一个三元语句,它是一行if语句。。零?是一个布尔函数,如果值为n则返回true,否则返回false。它首先检查函数是否为true或false。然后执行if / else来赋值(如果.nil?函数返回true,它将nil作为值,否则它将File.join(root_dir,'/')作为值。

It can be rewritten like so:

它可以像这样重写:

if root_dir.nil?
  prefix = nil
else
  prefix = File.join(root_dir, '/')
end

#2

This is called a ternary operator and is used as a type of shorthands for if/else statements. It follows the following format

这称为三元运算符,用作if / else语句的一种缩写。它遵循以下格式

statement_to_evaluate ? true_results_do_this : else_do_this

A lot of times this will be used for very short or simple if/else statements. You will see this type of syntax is a bunch of different languages that are based on C.

很多时候,这将用于非常简短的if / else语句。您将看到这种语法是一堆基于C语言的不同语言。

#3

The code is the equivalent of:

代码相当于:

if root_dir.nil? 
  prefix = nil 
else 
  prefix = File.join(root_dir, '/')
end

See a previous question

查看上一个问题

#1