RubyKaigi 2017 の LT での発表資料です。

1. How to specify
frozen_string_literal: true
Kazuhiro NISHIYAMA
RubyKaigi 2017 LT
2017/09/19
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2. self.introduce
One of Ruby committers
Twitter, GitHub: @znz
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3. What’s frozen_string_literal
magic comment
Specify string literals are frozen or not per file
Frozen string literals are faster
Generate less objects
Reduce GC
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4. Example
After coding if exist
example:
# -*- coding: utf-8 -*-
# frozen_string_literal: true
p ''.frozen? #=> true
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5. Past release
Add frozen_string_literal: false for almost
*.rb files when Ruby 2.3.0
For compatibility with --enable=frozen-string-
literal command line option of ruby
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6. Changes in this year
Recent Ruby programs tend to specify true, but
ruby standard libraries are false.
So I changed to frozen_string_literal: true in
some files which assigned to no maintainer in doc/
maintainers.rdoc.
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7. Review points before change
Almost RuntimeError: can't modify frozen String
points are:
String#<<
bang methods (e.g. String#sub!)
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8. Overlooked modification
IO#read(length, out_buffer)
this buffer is overlooked
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9. Find modified string literal
--debug=frozen-string-literal command line
option is very useful
examples:
ruby --debug=frozen-string-literal test.rb
make test-all TESTS='-v base64' RUBYOPT=--debug=frozen-string-literal
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10. Tests
--debug=frozen-string-literal needs to run
codes.
So tests are very important.
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11. No change if can’t
If no tests, there is no need to forcibly change it.
I think working codes are useful than broken
faster codes.
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12. mkmf.rb
mkmf.rb has many tests
But mkmf.rb is too complex to me in a short time
So I remain false
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13. Conclusion
No tests may overlook modifications
Use frozen_string_literal: true if you can
You can use frozen_string_literal: false in
some cases for compatibility for --enable=frozen-
string-literal
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