Navigating to safe navigation

2018-05-29T13:12:57+00:00

In December 2013, Ruby 2.3 was released and introduced a safe navigation operator to the language: &.. The behavior of the operator is identical to ActiveSupport’s try!:

toast = []
# Both lines below push to the array
toast.try!(:push, '🥑')
toast&.push('🥑')

toast = ""
# Both lines below raise NoMethodError
toast.try!(:push, '🥑')
toast&.push('🥑')

toast = nil
# Both lines below return nil
toast.try!(:push, '🥑')
toast&.push('🥑')

In the Rails projects I work on, try! is used extensively, so this new operator quickly caught my eye.

Curious to see how &. is implemented, I looked up the patch and noticed that it’s written entirely in C, unlike try! which is written in Ruby. Knowing this, I was curious if there is any performance benefit to migrate to &., so I threw together a benchmark:

require "benchmark"
require "active_support/all"

Benchmark.bm(14) do |x|
  count = 10_000_000

  x.report("nil.try!(:length)") do
    count.times { nil.try!(:length) }
  end

  x.report("'a'.try!(:length)") do
    count.times { 'a'.try!(:length) }
  end

  x.report("nil&.length      ") do
    count.times { nil&.length }
  end

  x.report("'a'&.length      ") do
    count.times { 'a'&.length }
  end
end

Here are the results on my machine:

                     user     system      total        real
nil.try!(:length)  1.700000   0.080000   1.780000 (  1.786330)
'a'.try!(:length)  3.170000   0.130000   3.300000 (  3.312468)
nil&.length        0.380000   0.000000   0.380000 (  0.380821)
'a'&.length        0.820000   0.050000   0.870000 (  0.872184)

Wow, &. is 4x faster than try!! Upon learning this, I went to regex hell and back and wrote a one line shell script to automatically convert usages of try! to &. in all Ruby/HAML files in the current directory and subdirectories:

find . \
  -type f \
  \( -name '*.rb' -o -name '*.haml' \) \
  -exec sed -i 's/\.try!(:\([^,)]\+\))/\&.\1/g' '{}' \; \
  -exec sed -i 's/\.try!(:\([^,)]\+\)\, *\([^)]\+\)\?)/\&.\1(\2)/g' '{}' \;

Note: this assumes GNU sed, so if you’re on MacOS you’ll need to brew install gnu-sed and replace sed calls with gsed.

Hopefully this one-liner will help you migrate too!

‽

Navigating to safe navigation