migrate_to_frozen_string_literal

[20220613 update] better use robocop auto-correct to handle this issue.

I’ve read a blog post written by Mike Perham introducing the Magic Comment, and I tried it out in my project.

The # frozen_string_literal: true

STEP-1: add this “magic comment”

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# Find all ruby files.
# Iterate through them.
# Add two lines if the file doesn't have those magic comment.

basedir = Rails.root.to_s
filenames = Dir["#{basedir}/**/*.rb"]
target = "# frozen_string_literal: true"

filenames.each do |filename|
lines = File.foreach(filename).first(2)

if lines != ["#{target}\n", "\n"]
`gsed -i "1i#{target}" "#{filename}"` # Use gsed on macos.
`gsed -i "1G" "#{filename}"` # Use sed on linux.
end
end

STEP-2: do automated/manual tests

This is important, since your project code may have a situation for manipulating Mutable String.

STEP-3: deploy and pay extra attention to production state

Be ready to rollback your deployment. You know, shit happens.

Exception occurred: FrozenError

Yes, it happened…

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{
"class": "ScanAlertingAndPendingWorker",
"args": [],
"retry": 1,
"queue": "default",
"jid": "0a48de6e85b383432760b013",
"created_at": 1646124005.491867,
"enqueued_at": 1646124034.8366895,
"error_message": "can't modify frozen String",
"error_class": "FrozenError",
"failed_at": 1646124035.9765105,
"retry_count": 0,
}

Occurrence No.1

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# frozen_string_literal: true

content = ""
content << 'world'
content << 'hello'

solution

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# frozen_string_literal: true

content = String.new
content << 'world'
content << 'hello'

Occurrence No.2

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# frozen_string_literal: true

body = 'Roses are red Mud is fun'
body.force_encoding('utf-8')

solution

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# frozen_string_literal: true

body = 'Roses are red Mud is fun'
body.dup.force_encoding('utf-8')
# or
String.new(body).force_encoding('utf-8')

At Last

But to my disappointment, I didn’t see significant memory reduction.

It might be related to the size of the system.(Is it?)