Just a small benchmark to clear up the myth, Ruby wouldn'd garbage collect any Symbols. In fact, MRI 2.2.0 introduced Symbol GC in December 2014 (see notable changes in the release announcement).
The benchmark is quite simple: It basically cretes a bunch of Symbols via String#to_sym and counts Symbol::all_symbols afterwards.
I've used rbenv to test the Symbol GC (or the lack thereof) of these interpreter implementations:
| random_twitter_message = (1..140).map{ rand 0xFF }.pack("C*") | |
| hexdump random_twitter_message | |
| # 0000: af 98 02 2b 25 13 01 42 b8 cd 3a a5 23 07 c2 43 |...+%..B ..:.#..C| | |
| # 0010: c0 af bd 65 3e a7 c0 4c 26 b9 1e 54 cc c3 5b 3f |...e>..L &..T..[?| | |
| # 0020: db d6 86 76 22 d4 31 ab 32 fe b6 32 f4 d4 1c 01 |...v".1. 2..2....| | |
| # 0030: f6 5d 25 8c 64 9b 18 3a 9d 50 14 a2 86 79 a6 f2 |.]%.d..: .P...y..| | |
| # 0040: da 50 f3 70 b6 bc e4 76 15 db 2f b7 f6 9c 88 d0 |.P.p...v ../.....| | |
| # 0050: 63 95 23 66 b3 20 f6 ab 62 a6 28 92 c7 6d a9 e0 |c.#f. .. b.(..m..| | |
| # 0060: 1c 2d fe 12 3e fd 8b 95 47 4d b2 14 07 e8 6b 6c |.-..>... GM....kl| |
| -# app/views/devise/registrations/edit.html.haml | |
| %h1.page-header | |
| Edit | |
| = resource_name.to_s.humanize | |
| = form_for resource, as: resource_name, url: registration_path(resource_name), html: { method: :put, class: 'form-horizontal' } do |f| | |
| = devise_error_messages! | |
| .form-group |
| $ ruby -v | |
| ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-linux] | |
| $ ruby re_bench.rb | |
| Rehearsal -------------------------------------------------------- | |
| (?-mix:^[a-zA-Z]$) 0.780000 0.000000 0.780000 ( 0.783924) | |
| (?i-mx:^[a-z]$) 0.790000 0.000000 0.790000 ( 0.789410) | |
| (?-mix:\A[a-zA-Z]\z) 0.370000 0.000000 0.370000 ( 0.373894) | |
| (?i-mx:\A[a-z]\z) 0.370000 0.000000 0.370000 ( 0.373349) | |
| ----------------------------------------------- total: 2.310000sec |