How to do “late” string interpolation in Ruby

Question

>> string = \'#{var}\'
=> \"\\#{var}\"

>> proc = Proc.new { |var| string }
=> #

>> proc.call(123)
=> \"\\         


        

Answer 1

Although this is possible, it's not going to work how you intend here without having to use eval, and generally that's a bad idea if there's an alternative. The good news is you have several options.

The most straightforward is to use sprintf formatting which is made even easier with the String#% method:

string = '%s'

proc = Proc.new { |var| string % var }

proc.call(123)
# => "123"

This is a really reliable method as anything that supports the .to_s method will work and won't cause the universe to implode if it contains executable code.