Ruby:带字符串插值的eval [英] Ruby: eval with string interpolation

问题描述

我不明白，为什么eval如此工作:

I don't understand, why eval works like this:

"123 #{456.to_s} 789" # => "123 456 789"
eval('123 #{456.to_s} 789') # => 123

如何在eval内部插入字符串?

How can I interpolate into a string inside eval?

更新:

谢谢你，朋友们.有效.

Thank you, friends. It worked.

因此，如果您要稍后评估带有#{}的字符串变量，则应按以下说明进行操作:

So if you have a string variable with #{} that you want to eval later, you should do it as explained below:

string = '123 #{456} 789' 
eval("\"" + string + "\"")
# => 123 456 789

或

string = '123 #{456} 789' 
eval('"' + string + '"')
# => 123 456 789

推荐答案

发生了什么事，eval正在将字符串作为源代码进行评估.当您使用双引号时，字符串将被内插

What's happening, is eval is evaluating the string as source code. When you use double quotes, the string is interpolated

eval '"123 #{456.to_s} 789"'
# => "123 456 789"

但是，当您使用单引号时，不会进行插值，因此#会开始注释，并且您会得到

However when you use single quotes, there is no interpolation, hence the # starts a comment, and you get

123 #{456.to_s} 789
# => 123

字符串内插发生在eval调用之前，因为它是方法的参数.

The string interpolation happens before the eval call because it is the parameter to the method.

还请注意，456.to_s是不必要的，您可以执行#{456}.

Also note the 456.to_s is unnecessary, you can just do #{456}.

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