Ruby Quirks: String#[]
In the series of posts that have Ruby Quirks in the title, my goal is to keep track of unexpected behaviors I encounter with Ruby as I continue learning the language. I will divide the quirks into separate sections (most likely respective classes) as I encounter them. Since it is the same post, that will be constantly updated, I will put the date I encountered a particular quirk next to it’s subheading. I am going to take Pete’s advice and write separate posts for each quirk I encounter.
Quirk Information
Class: String
Operator: []
String class has [] operator that allows us to get a substring for a given string. For example:
name = "Ashish"
str = name[2,3] # str contains "his"
However, if you pass a single index to the [] operator, the response is not something you would expect. For example:
char = name[1] # char contains 115, the ASCII representation of the character s
While we are in the topic of characters & their ASCII representation, Ruby provides a ? operator to evaluate the ASCII representation of a string. For example:
?a # returns 97
?A # returns 65
?s # returns 115
?AA # results in SyntaxError
This quirk can be seen in Ruby 1.8.7 & earlier versions of Ruby. However, from 1.9.1, the behavior is as expected. For example, in 1.9.1 and beyond:
?a # returns a
"Ashish"[1] # returns s
String#[] also allows you to pass a regexp as the first argument, and an integer index of matches as the second. This is very handy if you want to use a regexp to get a substring of a string.
I did something similar to this the other day at work:
>> url = “http://www.google.com/search?q=ruby”
=> “http://www.google.com/search?q=ruby”
>> url[ /https?:\/\/([^\/]+)/, 1 ]
=> “www.google.com”
String#[] is aliased as String#slice, and there are a few other tricks waiting in the docs for you.
pete
July 10, 2010 at 7:30 pm
That definitely sounds handy. Thanks!
tundal45
July 10, 2010 at 8:45 pm
Also, I would recommend writing new posts for new ruby quirks, so that anyone following your rss feed can be updated about the change. I’d certainly like it better.
pete
July 10, 2010 at 7:32 pm
Yeah. I was not thinking clearly initially. I think if I tag them all Ruby Quirks, I can have them all listed in one page while them being separate posts. I will change that. Thanks for the advice & thanks for reading!
tundal45
July 10, 2010 at 8:46 pm