Ruby do/end 与大括号
为什么这个映射表达式会根据我使用大括号还是 do/end 产生不同的结果？
a = [1,2,3,4,5]
p a.map { |n|
n*2
}
#=> [2,4,6,8,10]
p a.map do |n|
n*2
end
#=> [1,2,3,4,5]
Why does this map expression produce different results depending on whether I use braces or do/end?
a = [1,2,3,4,5]
p a.map { |n|
n*2
}
#=> [2,4,6,8,10]
p a.map do |n|
n*2
end
#=> [1,2,3,4,5]
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这是因为第二行被解释为：
而不是：
在这种情况下，语法是模棱两可的，而
do似乎并不像{那样强烈。That's because the second line is interpreted as:
instead of:
The grammar is ambiguous in this case and
dodoesn't seem to bind as strongly as{.这与
{字符和do关键字的关联性差异有关。在第一种情况下，块被解释为
map函数的块参数。 map 函数的结果是p函数的参数。在第二种情况下，该块被解释为
p函数的块参数，而a.map被解释为p< /代码> 函数。由于a.map的计算结果为a，因此会打印原始数组。在这种情况下，该块实际上被忽略。That has to do with the difference in associativity of the
{character and thedokeyword.In the first case, the block is interpreted as a block argument to the
mapfunction. The result of the map function is the argument to thepfunction.In the second case, the block is interpreted as a block argument to the
pfunction, while thea.mapis interpreted as the first argument to thepfunction. Sincea.mapevaluates toa, this prints the original array. The block is effectively ignored in this case.使用 do/end 语法，您可以将块作为第二个参数传递给 p，而不是传递给映射。您会得到相同的结果：
该块被
p忽略，因为它不会在inspect上产生任何内容。With the
do/endsyntax you are passing the block topas a second argument, rather than to the map. You get the same result with:The block is ignored by
pas it does not produce anything oninspect.