[ActiveModel] Improve the performance of mass assignments

[shotat]

Summary

Improve the performance of ActiveModel initializer with removing duplicated string object generation.

Other Information

simple benchmarks for ActiveModel::new

1.2x faster than the current implementation.

before     31.132k (± 5.2%) i/s -    157.781k in   5.083369s
after      37.170k (± 4.7%) i/s -    185.614k in   5.006230s

[jonathanhefner]

Although I honestly enjoy micro-optimizing, this change will probably have no effect outside of a microbenchmark. Have you tested it in a larger context?

Also, String#freeze would be more idiomatic. EDIT: It was late, and I wasn't thinking straight. String#freeze isn't really applicable when using interpolated strings.

[shotat]

@jonathanhefner
Thanks. I agree with your opinion. There might be no effect on a typical Rails app.

However, ActiveModel is used in various contexts independent of Rails.
This change benefits on batch processing like data format conversions using ActiveModel.

[rafaelfranca]

Thank for the pull request but could you just put # frozen_string_literal: true to the top of the file? Or the performance improvement come from avoiding to do the interpolation twice?

[kaspth]

What's the diff if we use quoted symbols :#{k}=?

[shotat]

@rafaelfranca
Thanks, I just put # frozen_string_literal: true.
The problem was unnecessary repeated string interpolations as you mentioned.

@kaspth
Thanks. I noticed that quoted symbols are better as a whole.
Following reflection methods(respond_to? and public_send) handles symbols faster than strings.

 after     40.172k (± 2.6%) i/s -    203.149k in   5.060347s
before     32.679k (± 4.0%) i/s -    163.929k in   5.025078s