'=>' 的 Ruby 语法 [英] Ruby Syntax of '=>'

问题描述

在带有散列的 ruby​​ 中使用 => 似乎很简单:

The use of => in ruby with hashes seems straightforward:

a = {key1: => value1, key2: => value2}
b = {"key1" => value1, "key2" => value2}

Ruby 使用了相当多的语法糖.这是一个示例代码块

Ruby makes quite a little bit of use of syntactic sugar. Here's an example code block

begin
   [some code]
rescue Exception => e
   [some error handling code]
end

救援线到底发生了什么，特别是在 Exception 和变量 e 之间以及 => 之间?rescue 是保留关键字，e 显然是一个变量.其余的部分?在这种情况下=>的作用是什么?

What exactly is going on in the rescue line, particularly between Exception and the variable e with the => in between? rescue is a reserved keyword, e is clearly a variable. The rest? What is the function of => in this case?

更新每个人似乎都没有抓住重点.我知道救援异常 => e"与哈希无关.我想从语法上知道该行中发生了什么.

Update Everyone appears to be missing the point. I know "rescue Exception => e" has nothing to do with hashes. I want to know syntactically what is going on in that line.

rescue"一词是关键字保留字，是 ruby​​ 语言的一部分.我很确定e"是一个变量，在功能上也可以是a"、b"或c".什么是异常"和=>"?有没有另一种方式来写这个表达式，让像我这样的人更容易理解，他在编程时只学习语法严格且没有语法糖的语言?

The word "rescue" is a keyword reserved word and is part of the ruby language. I'm pretty sure "e" is a variable, and could just as functionally be "a", "b", or "c". What are "Exception" and "=>"? Is there another way to write this expression to make it more intelligible to a guy like me who cut his programming teeth on languages with rigid syntax and no syntactic sugar?

推荐答案

默认情况下，rescue 只救援 RuntimeError，这也是 raise 的默认类，没有明确的异常类声明:

By default, rescue only rescues RuntimeError, which is also a default class for raise without an explicit exception class declaration:

begin
  raise "foo"
rescue
  puts "rescued"
end

如果需要访问异常实例，可以使用以下语法:

If there is a need to get an access to the exception instance, one might use the following syntax:

begin
  raise "foo"
rescue => e
  puts "rescued #{e.message}"
end

也可以在不同的子句中拯救不同的异常:

One also might rescue different exceptions in different clauses:

class Error1 < RuntimeError; end
class Error2 < RuntimeError; end

begin
  [some code]
rescue Error1 => e
  puts "rescued an instance of Error1: #{e.message}"
rescue Error2 => e
  puts "rescued an instance of Error2: #{e.message}"
rescue => e # standard RuntimeError
  puts "rescued a generic error: #{e.message}"
end

也就是说，这种语法与哈希无关，它用于区分许多rescue块中的不同异常类.

That said, this syntax has nothing to do with hashes and it’s used to distinguish between different exception classes in many rescue blocks.

在您的示例中，有一个 Exception(它不是 RuntimeError 的后继者，并且默认情况下未获救)已获救.虽然它被认为是一种不好的做法(因为这里的边距太小而无法描述)，但有时它仍然有用.

In your example, there is an Exception (which is not a successor of RuntimeError and is not rescued by default) rescued. While it’s considered to be a bad practice (for the reasons margins here are too tiny to describe,) sometimes it’s still of some use.

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