Ruby块采用数组或多个参数 [英] Ruby block taking array or multiple parameters

问题描述

今天，我很惊讶地发现ruby会自动找到作为块参数给出的数组的值.

Today I was surprised to find ruby automatically find the values of an array given as a block parameter.

例如:

foo = "foo"
bar = "bar"
p foo.chars.zip(bar.chars).map { |pair| pair }.first #=> ["f", "b"]
p foo.chars.zip(bar.chars).map { |a, b| "#{a},#{b}" }.first #=> "f,b"
p foo.chars.zip(bar.chars).map { |a, b,c| "#{a},#{b},#{c}" }.first #=> "f,b,"

我希望最后两个示例会出现某种错误.

I would have expected the last two examples to give some sort of error.

1. 这是红宝石中更笼统的概念的例子吗?
2. 我不认为我在问题开头的措辞是正确的，我怎么称呼这里发生的事情?

推荐答案

Ruby的块机制对其有一个怪癖，也就是说，如果要遍历包含数组的内容，则可以将它们扩展为不同的变量:

Ruby's block mechanics have a quirk to them, that is if you're iterating over something that contains arrays you can expand them out into different variables:

[ %w[ a b ], %w[ c d ] ].each do |a, b|
  puts 'a=%s b=%s' % [ a, b ]
end

此模式在使用Hash#each时非常有用，并且您希望分解成对的key和value部分:each { |k,v| ... }在Ruby代码中非常常见.

This pattern is very useful when using Hash#each and you want to break out the key and value parts of the pair: each { |k,v| ... } is very common in Ruby code.

如果您的块接受多个参数 ，并且要迭代的元素是一个数组，那么它将切换如何解释参数.您可以随时强制展开:

If your block takes more than one argument and the element being iterated is an array then it switches how the arguments are interpreted. You can always force-expand:

[ %w[ a b ], %w[ c d ] ].each do |(a, b)|
  puts 'a=%s b=%s' % [ a, b ]
end

这对于复杂的情况很有用:

That's useful for cases where things are more complex:

[ %w[ a b ], %w[ c d ] ].each_with_index do |(a, b), i|
  puts 'a=%s b=%s @ %d' % [ a, b, i ]
end

由于在这种情况下，它遍历数组和附加的元素，所以每个项目实际上都是内部为%w[ a b ], 0形式的元组，如果您需要块仅接受一个参数.

Since in this case it's iterating over an array and another element that's tacked on, so each item is actually a tuple of the form %w[ a b ], 0 internally, which will be converted to an array if your block only accepts one argument.

这与定义变量时可以使用的原理大致相同:

This is much the same principle you can use when defining variables:

a, b = %w[ a b ]
a
# => 'a'
b
# => 'b'

这实际上为a和b分配了独立的值.与此相反:

That actually assigns independent values to a and b. Contrast with:

a, b = [ %w[ a b ] ]
a
# => [ 'a', 'b' ]
b
# => nil

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