ruby 中的无效函数 [英] Invalid function in ruby

问题描述

为什么这个函数无效?

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

end

意外的 ')' 期待 keyword_end

unexcpected ')' expecting keyword_end

谢谢！

推荐答案

在 Ruby 中，不能用可选参数包围必需参数.使用

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

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

将解决问题.

作为一个思想实验，考虑原始函数

As a thought experiment, consider the original function

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

如果我将该方法称为request(object)，则所需的行为是相当明显的——以object 作为resource 调用该方法> 参数.但是如果我把它称为 request('post', object) 呢?Ruby 需要理解 method 的语义来决定 'post' 是 method 还是 resource，以及 object 是 resource 还是 meta.这超出了 Ruby 解析器的范围，因此它只会抛出无效函数错误.

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.

一些额外的提示:

我也会把 meta 参数放在最后，它允许你在没有花括号的情况下传递哈希选项，例如:

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')

正如 Andy Hayden 在评论中指出的那样，以下函数有效:

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

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

将所有可选参数放在函数的末尾通常是一种很好的做法，以避免在调用此类函数时产生心理体操.

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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