前缀的意义是什么？ Ruby 1.9中的运算符

Question

I'm just wondering what applications it has. I believe in 1.9 the prefix ? would return the string version of that character.

?a   #=> "a"
?\t  #=> "\t"

Is this just shorthand for 'a' or '\\t'?

Answer 1

It's mainly for backwards compatibility. In versions prior to 1.9, ? evaluated to a Fixnum corresponding to the ASCII value of the character in question. Indexing into a String also returned a Fixnum .

So, if you wanted to check, for example, if the third character of a string was the letter 'a' you would do

s[2] == ?a

In Ruby 1.9, strings are no longer treated as an array of fixnums but as an iterator of characters (single-character strings, actually). As a result, the above code would no longer work: s[2] would be a string, ?a would be a number, and those two would never be equal.

Therefore, ? was also changed to evaluate to a single-character string, so that the above code continues to work.

Answer 2

in ruby 1.8 and earlier

?a 

would return the ASCII version of 'a' char.

in 1.9 it just returns the string ( just as you've assumed )

Answer 3

You are correct, you get the string value of the characters. It was previously used to get the ASCII value of the characters.