Is there any advantage to _ever_ using a single quote around a string in Ruby/Rails?

Question

I understand the functional difference between single and double quotes in Ruby, but I'm wondering what concrete reasons people have for varying between the two. In my mind it seems like you should just always use a double quote, and not think about it.

A couple rationales that I've read in researching the topic...

1. Use a single quote unless a double quote is required.

2. There's a very, very minor performance advantage to a single quotes.

Any other interesting thoughts out there? (Or maybe this is a case of the freedom or Ruby leaving the door open for no One Right Way to do something...)

Answer 1

I usually follow the following rule:

never use double quotes (or %Q or %W) if you don't interpolate

The reason for this is that if you're trying to track down an error or a security bug, you immediately know when looking at the beginning of the string that there cannot possibly any code inside it, therefore the bug cannot be in there.

However, I also follow the following exception to the rule:

use double quotes if they make the code more readable

I.e. I prefer

"It's time"

over

'It\'s time'
%q{It's time}

It is technically true that single quoted strings are infinitesimally faster to parse than double quoted strings, but that's irrelevant because

• the program only gets parsed once, during startup, there is no difference in runtime performance
• the performance difference really is extremely small
• the time taken to parse strings is irrelevant compared to the time taken to parse some of Ruby's crazier syntax

So, the answer to your question is: Yes, there is an advantage, namely that you can spot right away whether or not a string may contain code.

Answer 2

I can think of three reasons to use single quoted strings:

1. They look cleaner (the reason I use them)
2. They make it easier to create a string you'd otherwise have to escape ('he said "yes"' vs "he said \"yes\"")
3. They are slightly more performant.

Answer 3

I would assume using a single-quoted string is faster, since double quotes allow string interpolation, and single-quoted strings do not.

That's the only difference I know of. For that reason, it's probably best to only use a single-quoted string unless you need string interpolation:

num = 59
"I ate #{num} pineapples"`