2台MYSQL服务器集群配置
2008-08-22 22:57
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class variables are available in class methods and instance methods, but class instance variable is only available in class methods:
ruby 代码
class Test
@@cla_var = 1
@inst_var = 1
def self.cla_var
@@cla_var
end
def cla_var
@@cla_var
end
def self.inst_var
@inst_var
end
def inst_var
#here @inst_var is treated as the instance variable not class instance variable
@inst_var
end
end
Class variables are shared by children of the class in which they are first defined, but class instance variables not, every child has it's own copy of class instance variable(Rumor has it that ruby1.9 will change this).
ruby 代码
class Parent
@@cla_var = 1
@inst_var = 2
def self.cla_var
@@cla_var
end
def self.inst_var
@inst_var
end
def self.cla_var=(cla_var)
@@cla_var = cla_var
end
def self.inst_var=(inst_var)
@inst_var = inst_var
end
end
class Child1 < Parent
end
class Child2 < Parent
end
#class variables are shared by parent and all the children
>> Parent.cla_var
=> 1
>> Child1.cla_var
=> 1
>> Child2.cla_var
=> 1
>> Child1.cla_var = 3
=> 3
>> Parent.cla_var
=> 3
>> Child2.cla_var
=> 3
#every children has it's own copy of class instance variables
>> Parent.inst_var
=> 2
>> Child1.inst_var
=> nil
>> Child2.inst_var>> Child1.inst_var = 4
=> 4
>> Parent.inst_var
=> 2
>> Child2.inst_var
=> nil
=> nil
ruby 代码
class Test
@@cla_var = 1
@inst_var = 1
def self.cla_var
@@cla_var
end
def cla_var
@@cla_var
end
def self.inst_var
@inst_var
end
def inst_var
#here @inst_var is treated as the instance variable not class instance variable
@inst_var
end
end
Class variables are shared by children of the class in which they are first defined, but class instance variables not, every child has it's own copy of class instance variable(Rumor has it that ruby1.9 will change this).
ruby 代码
class Parent
@@cla_var = 1
@inst_var = 2
def self.cla_var
@@cla_var
end
def self.inst_var
@inst_var
end
def self.cla_var=(cla_var)
@@cla_var = cla_var
end
def self.inst_var=(inst_var)
@inst_var = inst_var
end
end
class Child1 < Parent
end
class Child2 < Parent
end
#class variables are shared by parent and all the children
>> Parent.cla_var
=> 1
>> Child1.cla_var
=> 1
>> Child2.cla_var
=> 1
>> Child1.cla_var = 3
=> 3
>> Parent.cla_var
=> 3
>> Child2.cla_var
=> 3
#every children has it's own copy of class instance variables
>> Parent.inst_var
=> 2
>> Child1.inst_var
=> nil
>> Child2.inst_var>> Child1.inst_var = 4
=> 4
>> Parent.inst_var
=> 2
>> Child2.inst_var
=> nil
=> nil
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