Ruby: eval with string interpolation

Question

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

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


        

Answer 1

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"

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

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

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

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