what is a symble in Ruby?

:north
:a
:aSymble

它就是一個不需要 value (有值）, 但要代表一個與衆不同的 id.

demo:


$ irb
irb(main):001:0> :north
=> :north
irb(main):002:0> a = :north
=> :north
irb(main):003:0> b = :north
=> :north
irb(main):004:0> a == b
=> true
irb(main):005:0> :north = 1
SyntaxError: compile error
(irb):5: syntax error, unexpected '=', expecting $end
:north = 1
^
from (irb):5
from :0
irb(main):006:0> puts :north
north
=> nil
irb(main):007:0> puts :north.to_s
north
=> nil
irb(main):008:0> :north == :north
=> true
irb(main):009:0> a == :north
=> true
irb(main):010:0> a = :north
=> :north
irb(main):011:0> a == :north
=> true
irb(main):012:0>