String concatenation and Ruby

Question

Hi,

I am looking for a more elegant way of concatenating strings in Ruby.

I have the following line:

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

Is there a nicer way of doing this?

And for that matter what is the difference between << and +?

Thanks

Answer 1

I guess

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

should do the trick.

Answer 2

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"

2/ seems to be more efficient in term of memory/speed from what I've seen (not measured though).

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.

Answer 3

You might get away with:

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

Answer 4

Since this is a path I'd probably use array and join:

source = [ROOT_DIR, project, 'App.config'] * '/'

Answer 5

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

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

Answer 6

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"

Answer 7

I'd prefer using Pathname:

require 'pathname' # pathname is in stdlib
Pathname(ROOT_DIR) + project + 'App.config'

about << and + from ruby docs:

+: Returns a new String containing other_str concatenated to str

<<: Concatenates the given object to str. If the object is a Fixnum between 0 and 255, it is converted to a character before concatenation.

so difference is in what becomes to first operand (<< makes changes in place, + returns new string so it is memory heavier) and what will be if first operand is Fixnum (<< will add as if it was character with code equal to that number, + will raise error)