字符串连接错误
我遇到了语法错误。我承认这是一个语法错误，但我有点好奇为什么这是一个语法错误。
这完全按照你的预期工作：
(0..9).each { |n| puts n.to_s + "^2 = " + (n**2).to_s }
这会抛出一个错误：
(0..9).each { |n| puts n.to_s +"^2 = "+ (n**2).to_s }
错误：
NoMethodError: undefined method '+@' for "^2 = ":String
奇怪的是，我可以将第二个加号移动到任何地方，Ruby 似乎没有问题，但如果第一个加号碰巧触及双引号，我收到语法错误。
究竟为什么会发生这种情况？
I ran into a syntax error. I accept that it's a syntax error, but I'm somewhat curious as to why it's a syntax error.
This works exactly as you'd expect it to:
(0..9).each { |n| puts n.to_s + "^2 = " + (n**2).to_s }
This throws an error:
(0..9).each { |n| puts n.to_s +"^2 = "+ (n**2).to_s }
The error:
NoMethodError: undefined method '+@' for "^2 = ":String
Oddly, I can move the second plus sign wherever and Ruby seems to have no problem with it, but if that first one happens to touch the double quote, I get a syntax error.
Why exactly does this happen?
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n.to_s +"^2 = "被解析为n.to_s(+"^2 = ")，它在语法上是有效的，意思是“执行一元加运算”字符串^2 =上，然后将结果作为参数传递给to_s”。但是，由于字符串没有一元加法运算（由+@方法表示），因此您会收到NoMethodError（不是语法错误）。以这种方式解析而不是
n.to_s() + "^2 = "的原因是，如果以这种方式解析，则puts +5或puts -x还必须解析为puts() + 5和puts() - x而不是puts(+5)和puts(-x) - 在该示例中很明显后者就是我们的意图。n.to_s +"^2 = "is parsed asn.to_s(+"^2 = "), which is syntactically valid and means "perform the unary plus operations on the string^2 =and then pass the result as an argument toto_s". However since strings don't have a unary plus operation (represented by the method+@), you get aNoMethodError(not a syntax error).The reason that it's parsed this way and not as
n.to_s() + "^2 = "is that if it were parsed this way thenputs +5orputs -xwould also have to be parsed asputs() + 5andputs() - xrather thanputs(+5)andputs(-x)- and in that example it's rather clear that the latter is what was intended.