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Ruby Strings vs Symbols

Minh / 22 Apr 2019

Định nghĩa

"hello" # String
:hello # Symbol

"hello world!" # String with space and bang!
"hello world!".to_sym # String can convert to Symbol and vice versa
# => :"hello world!"
:"hello world!".class
# => Symbol
# Vậy là Symbol cũng có thể chưa kí tự đặc biệt

Symbol can’t change while mutable String can

a = "hello"
# => "hello"
b = :hello
# => :hello
a.object_id
# => 47213907316480
b.object_id
# => 1150428
a << "w"
# => "hellow"
a.object_id
# => 47213907316480
b << "w"
# NoMethodError: undefined method `<<' for :hello:Symbol

Frozen Strings: immutable String

example = "hello world"
example.upcase!

puts example

example.freeze
example.downcase!

# => "HELLO WORLD"
# => *.rb:7:in `downcase!': can't modify frozen string (TypeError)

Object ID

puts "hello world".object_id
puts "hello world".object_id
puts "hello world".object_id
puts "hello world".object_id
puts "hello world".object_id

# => 3102960
# => 3098410
# => 3093860
# => 3089330
# => 3084800

puts :"hello world".object_id
puts :"hello world".object_id
puts :"hello world".object_id
puts :"hello world".object_id
puts :"hello world".object_id

# => 239518
# => 239518
# => 239518
# => 239518
# => 239518

Performance

  • Khai báo Symbol nhanh hơn 40% so với khai báo String
  • So sánh Symbol vs Symbol nhanh hơn 40% so với so sánh String vs String

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