Ruby-on-rails Rails 3 中的字符串连接
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String concatenation in Rails 3
提问by valk
I'm wondering why this is so: Ruby concatenates two strings if there is a space between the plus and the next string. But if there is no space, does it apply some unary operator?
我想知道为什么会这样：如果加号和下一个字符串之间有空格，Ruby 会连接两个字符串。但是如果没有空格，它是否应用了一些一元运算符？
params['controller'].to_s + '/'
# => "posts/"
params['controller'].to_s +'/'
# => NoMethodError: undefined method `+@' for "/":String
回答by Matt Glover
The parser is interpreting +'/'as the first parameter to the to_smethod call. It is treating these two statements as equivalent:
解析器将解释+'/'为to_s方法调用的第一个参数。它将这两个语句视为等价的：
> params['controller'].to_s +'/'
# NoMethodError: undefined method `+@' for "/":String
> params['controller'].to_s(+'/')
# NoMethodError: undefined method `+@' for "/":String
If you explicitly include the parenthesis at the end of the to_smethod call the problem goes away:
如果您在to_s方法调用的末尾明确包含括号，问题就会消失：
> params['controller'].to_s() +'/'
=> "posts/"
回答by OneChillDude
If you want to concatenate a string, the safest way is to write "#{params[:controller].to_s} /"ruby's string escaping is safer and better in many cases
如果要拼接一个字符串，最安全的方式是写"#{params[:controller].to_s} /"ruby的字符串转义在很多情况下更安全更好
回答by Arup Rakshit
Look closely the error:
仔细看错误：
p "hi".to_s +'/'
p "hi".to_s -'2'
#=> in `<main>': undefined method `+@' for "/":String (NoMethodError)
This is because unary operator+,-etc is defined only Numericclass objects. It will be clear if you look at the code below:
这是因为unary operator+, -etc 只定义了Numeric类对象。如果你看看下面的代码就会很清楚：
p "hi".to_s +2
#=>in `to_s': wrong number of arguments (1 for 0) (ArgumentError)
Now the above error is exactly right for to_s. As to_sdoesn't take any argument when it is called.
现在上述错误完全适用于to_s. Asto_s被调用时不接受任何参数。
Correct version is:
正确的版本是：
p "hi".to_s + '2' #=> "hi2"
