String concatenation in Ruby

You can do that in several ways:

1. As you shown with << but that is not the usual way

2. With string interpolation

   source = "#{ROOT_DIR}/#{project}/App.config"
   

3. with +

   source = "#{ROOT_DIR}/" + project + "/App.config"
   

The second method seems to be more efficient in term of memory/speed from what I've seen (not measured though). All three methods will throw an uninitialized constant error when ROOT_DIR is nil.

When dealing with pathnames, you may want to use File.join to avoid messing up with pathname separator.

In the end, it is a matter of taste.

The + operator is the normal concatenation choice, and is probably the fastest way to concatenate strings.

The difference between + and << is that << changes the object on its left hand side, and + doesn't.

irb(main):001:0> s = 'a'
=> "a"
irb(main):002:0> s + 'b'
=> "ab"
irb(main):003:0> s
=> "a"
irb(main):004:0> s << 'b'
=> "ab"
irb(main):005:0> s
=> "ab"

If you are just concatenating paths you can use Ruby's own File.join method.

source = File.join(ROOT_DIR, project, 'App.config')