String concatenation in Ruby

Question

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

I have the following line:

source = \"#{ROOT_DIR}/\" << project <<          


        

Answer 1

Here are more ways to do this:

"String1" + "String2"

"#{String1} #{String2}"

String1<<String2

And so on ...

Answer 2

Here's another benchmark inspired by this gist. It compares concatenation (+), appending (<<) and interpolation (#{}) for dynamic and predefined strings.

require 'benchmark'

# we will need the CAPTION and FORMAT constants:
include Benchmark

count = 100_000


puts "Dynamic strings"

Benchmark.benchmark(CAPTION, 7, FORMAT) do |bm|
  bm.report("concat") { count.times { 11.to_s +  '/' +  12.to_s } }
  bm.report("append") { count.times { 11.to_s << '/' << 12.to_s } }
  bm.report("interp") { count.times { "#{11}/#{12}" } }
end


puts "\nPredefined strings"

s11 = "11"
s12 = "12"
Benchmark.benchmark(CAPTION, 7, FORMAT) do |bm|
  bm.report("concat") { count.times { s11 +  '/' +  s12 } }
  bm.report("append") { count.times { s11 << '/' << s12 } }
  bm.report("interp") { count.times { "#{s11}/#{s12}"   } }
end

output:

Dynamic strings
              user     system      total        real
concat    0.050000   0.000000   0.050000 (  0.047770)
append    0.040000   0.000000   0.040000 (  0.042724)
interp    0.050000   0.000000   0.050000 (  0.051736)

Predefined strings
              user     system      total        real
concat    0.030000   0.000000   0.030000 (  0.024888)
append    0.020000   0.000000   0.020000 (  0.023373)
interp    3.160000   0.160000   3.320000 (  3.311253)

Conclusion: interpolation in MRI is heavy.

Answer 3

Situation matters, for example:

# this will not work
output = ''

Users.all.each do |user|
  output + "#{user.email}\n"
end
# the output will be ''
puts output

# this will do the job
output = ''

Users.all.each do |user|
  output << "#{user.email}\n"
end
# will get the desired output
puts output

In the first example, concatenating with + operator will not update the output object,however, in the second example, the << operator will update the output object with each iteration. So, for the above type of situation, << is better.

Answer 4

You may use + or << operator, but in ruby .concat function is the most preferable one, as it is much faster than other operators. You can use it like.

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

Answer 5

You can concatenate in string definition directly:

nombre_apellido = "#{customer['first_name']} #{customer['last_name']} #{order_id}"

Answer 6

Concatenation you say? How about #concat method then?

a = 'foo'
a.object_id #=> some number
a.concat 'bar' #=> foobar
a.object_id #=> same as before -- string a remains the same object

In all fairness, concat is aliased as <<.