String concatenation in Ruby

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

<!-- language: lang-rb -->

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:

<!-- language: lang-none -->

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.

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.

You can also use `%` as follows:

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

This approach works with `'` (single) quotation mark as well.

You can concatenate in string definition directly:

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

For your particular case you could also use `Array#join` when constructing file path type of string:

string = [ROOT_DIR, project, 'App.config'].join('/')]

This has a pleasant side effect of automatically converting different types to string:

['foo', :bar, 1].join('/')
=>"foo/bar/1"

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"))

For Puppet:

```
$username = 'lala'
notify { "Hello ${username.capitalize}":
withpath => false,
}
```