Ruby 块语法错误

问题描述

可能的重复:
Ruby 块和非括号参数

我不确定我是否理解这个语法错误.我正在使用 Carrierwave 在 Rails 应用程序中管理一些文件上传，但我似乎错误地将块传递给其中一种方法.

I'm not sure I understand this syntax error. I'm using Carrierwave to manage some file uploads in a Rails app, and I seem to be passing a block to one of the methods incorrectly.

以下是 Carrierwave 文档中的示例:

version :thumb do
  process :resize_to_fill => [200,200]
end

这是我所拥有的:

version :full   { process(:resize_to_limit => [960, 960]) }
version :half   { process(:resize_to_limit => [470, 470]) }
version :third  { process(:resize_to_limit => [306, 306]) }
version :fourth { process(:resize_to_limit => [176, 176]) }

以上不起作用，我收到语法错误，意外的'}'，需要keyword_end.有趣的是，以下操作完美无缺:

The above doesn't work, I get syntax error, unexpected '}', expecting keyword_end. Interestingly enough, the following works perfectly:

version :full   do process :resize_to_limit => [960, 960]; end
version :half   do process :resize_to_limit => [470, 470]; end
version :third  do process :resize_to_limit => [306, 306]; end
version :fourth do process :resize_to_limit => [176, 176]; end

那么，我的问题是，为什么我可以使用 do...end 传递一个块，但在这种情况下不能使用大括号?

So, my question is, why can I pass a block using do...end but not braces in this instance?

谢谢！

推荐答案

试试这个:

version(:full)   { process(:resize_to_limit => [960, 960]) }
version(:half)   { process(:resize_to_limit => [470, 470]) }
version(:third)  { process(:resize_to_limit => [306, 306]) }
version(:fourth) { process(:resize_to_limit => [176, 176]) }

你有一个优先级问题.{ } 块比 do...end 块绑定得更紧密，比方法调用更紧密；结果是 Ruby 认为您试图提供一个块作为符号的参数，并说不.

You have a precedence problem. The { } block binds tighter than a do...end block and tighter than a method call; the result is that Ruby thinks you're trying to supply a block as an argument to a symbol and says no.

通过比较以下内容，您可以看到更清晰 (?) 或更熟悉的示例:

You can see a clearer (?) or possibly more familar example by comparing the following:

[1, 2, 3].inject 0  { |x, y| x + y }
[1, 2, 3].inject(0) { |x, y| x + y }

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