红宝石中的函数无效 [英] Invalid function in ruby

问题描述

  def request（method ='get'，resource，meta = {}，strip = true）
 
 end 
  

unexcpected'）'expected keyword_end

谢谢！

解决方案

在Ruby中，带可选参数的参数。使用

  def request（resource，method ='get'，strip = true，meta = {}）
 end 
  

将解决此问题。

一个想法实验，考虑原始函数

  def request（method ='get'，resource，meta = {}，strip = true）
 end 
  

如果我将该方法称为 request（对象），所需行为相当明显 - 用 object 作为资源参数。但是如果我把它称为 request（'post'，object）？ Ruby需要理解 method 的语义以决定'post'是否是方法或资源，以及 object 是资源或 meta 。这超出了Ruby解析器的范围，所以它只是抛出无效的函数错误。

一些附加提示：

我还会把元参数放在最后，它允许您在不加大括号的情况下传递哈希选项，例如：

  request（object，'get'，true，foo：'bar'，bing：'bang'）
  

正如Andy Hayden在评论中指出的那样，以下函数可以工作：

  def f （aa，a ='get'，b，c）;结束
  

将所有可选参数放在函数末尾以避免心理错误体操需要跟随这样的功能。

Why is this function invalid?

def request(method='get',resource, meta={}, strip=true)

end

unexcpected ')' expecting keyword_end

Thank you!

解决方案

In Ruby, you can't surround a required parameter with optional parameters. Using

def request(resource, method='get', strip=true, meta={})
end

will solve the issue.

As a thought experiment, consider the original function

def request(method='get',resource, meta={}, strip=true)
end

If I call that method as request(object), the desired behavior is fairly obvious -- call the method with object as the resource parameter. But what if I call it as request('post', object)? Ruby would need to understand the semantics of method to decide whether 'post' is the method or the resource, and whether object is the resource or the meta. This is beyond the scope of Ruby's parser, so it simply throws an invalid function error.

A couple additional tips:

I would also put the meta argument last, which allows you to pass the hash options in without curly braces, such as:

request(object, 'get', true, foo: 'bar', bing: 'bang')

As Andy Hayden pointed out in the comments, the following function works:

def f(aa, a='get', b, c); end

It's generally good practice to place all your optional parameters at the end of the function to avoid the mental gymnastics required to follow calls to a function like this.

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