ruby 中的并行分配对于两个等效代码片段的工作方式不同
下面的两个代码片段应该打印相同的内容，但事实并非如此。
ary = %W(1 2 5 6 B 8 5 4 6 5 6 9 7 A)
indx1 = 0...ary.index("B")
indx2 = (ary.index("A") + 1)..-1
ary[indx1], ary[indx2] = ary[indx2], ary[indx1]
puts ary.inspect
ary = %W(1 2 5 6 B 8 5 4 6 5 6 9 7 A)
ary[0...ary.index("B")], ary[(ary.index("A") + 1)..-1] = ary[(ary.index("A") + 1)..-1], ary[0...ary.index("B")]
puts ary.inspect
第一个打印：
["B", "8", "5", "4", "6", "5", "6", "9", "7", "A", nil, nil, nil, nil, "1", "2", "5", "6"]
第二个：
["B", "8", "5", "4", "6", "5", "6", "9", "7", "A", "1", "2", "5", "6"]
他们不应该打印相同的东西吗？他们似乎与我相当。
（使用 Mac OSX 10.6.7 和 ruby 1.9.2-p180）
The two code fragments below should print the same thing, but they don't.
ary = %W(1 2 5 6 B 8 5 4 6 5 6 9 7 A)
indx1 = 0...ary.index("B")
indx2 = (ary.index("A") + 1)..-1
ary[indx1], ary[indx2] = ary[indx2], ary[indx1]
puts ary.inspect
ary = %W(1 2 5 6 B 8 5 4 6 5 6 9 7 A)
ary[0...ary.index("B")], ary[(ary.index("A") + 1)..-1] = ary[(ary.index("A") + 1)..-1], ary[0...ary.index("B")]
puts ary.inspect
The first prints:
["B", "8", "5", "4", "6", "5", "6", "9", "7", "A", nil, nil, nil, nil, "1", "2", "5", "6"]
and the second:
["B", "8", "5", "4", "6", "5", "6", "9", "7", "A", "1", "2", "5", "6"]
Shouldn't they print the same thing? They seem equivalent to me.
(Using Mac OSX 10.6.7 and ruby 1.9.2-p180)
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它们是不同的，因为在第一种情况下，您预先计算索引，而在第二种情况下，您动态计算它们，并且数组在第一个分配和第二个分配之间变化。
从技术上讲，两个 RHS 评估都是在 LHS 分配之前进行的，但是两个 LHS 分配不能同时进行，因此在这种情况下，您实际上看到的
是相当于
所以您要做的第一件事是......
在这两种情况下。所以 ary 现在是
现在最初您将 indx1 和 indx2 分别计算为
0...4和14..-1，但现在如果您重新计算 indx1 和 indx2你将拥有的值：换句话说，
不再等于
也就是说，
给你
同时
给你
They're different because in the first case you're pre-calculating the indices, while in the second you're calculating them dynamically, and the array changes between the first assignment and the second.
Technically both RHS evaluations are made before the LHS assignments are made, but both LHS assignments can't be made simultaneously, so in this case you're effectively seeing that
is equivalent to
So the first thing you do is...
in both cases. So ary is now
Now originally you'd calculated indx1 and indx2 as
0...4and14..-1respectively, but now if you recalculated the indx1 and indx2 values you'd have:In other words,
is no longer equivalent to
That is,
gives you
while
gives you