[Rails] 分辨 symbol 和 string

resources :products do
  member do
    post :add_to_cart
  end
end

2.3.1 :001 > Symbol.all_symbols.count
 => 11064
2.3.1 :002 > who_name_is = "Jimmy"
 => "Jimmy"
2.3.1 :003 > Symbol.all_symbols.count
 => 11065
2.3.1 :006 > Symbol.all_symbols.map(&:to_s).include?("who_name_is")
 => true

2.3.1 :007 > who_name_is
 => Jimmy
 2.3.1 :010 > :who_name_is.object_id
 => 3572508
2.3.1 :014 > who_name_is = "Jimmy Tsai"
 => Jimmy Tsai
2.3.1 :024 > :who_name_is.object_id
 => 3572508

2.3.1 :025 > :who_name_is[0] = "k"
NoMethodError: undefined method `[]=' for :who_name_is:Symbol
Did you mean?  []
  from (irb):25
  from /Users/jimmy/.rvm/rubies/ruby-2.3.1/bin/irb:11:in `<main>'
2.3.1 :026 > :who_name_is[0]
 => "w"

2.3.1 :021 > :who_name_is = "jimmy Tsai"
SyntaxError: (irb):21: syntax error, unexpected '=', expecting end-of-input
:who_name_is = "jimmy Tsai"

2.3.1 :027 > "who_name_is"[0] = "k"
 => "k"

2.3.1 :001 > st = "jimmy"
 => "jimmy"
2.3.1 :002 > st.object_id
 => 70136566672520
2.3.1 :003 > :st.object_id
 => 3572508
2.3.1 :004 > st = "jimmy"
 => "jimmy"
2.3.1 :005 > st.object_id
 => 70136566640600
2.3.1 :006 > :st.object_id
 => 3572508