问题描述
>> a = 5
=> 5
>> b = a
=> 5
>> b = 4
=> 4
>> a
=> 5
如何将'b'设置为'a'，因此在示例中，变量a也将变为4.谢谢.
how can I set 'b' to actually be 'a' so that in the example, the variable a will become four as well. thanks.
推荐答案
class Ref
def initialize val
@val = val
end
attr_accessor :val
def to_s
@val.to_s
end
end
a = Ref.new(4)
b = a
puts a #=> 4
puts b #=> 4
a.val = 5
puts a #=> 5
puts b #=> 5
执行b = a时，b指向与a相同的对象(它们具有相同的object_id).
When you do b = a, b points to the same object as a (they have the same object_id).
执行a = some_other_thing时，a将指向另一个对象，而b保持不变.
When you do a = some_other_thing, a will point to another object, while b remains unchanged.
对于Fixnum，nil，true和false，如果不更改object_id，则无法更改该值.但是，您可以更改其他对象(字符串，数组，哈希等)而无需更改object_id，，因为您不使用赋值(=).
For Fixnum, nil, true and false, you cannot change the value without changing the object_id. However, you can change other objects (strings, arrays, hashes, etc.) without changing object_id, since you don't use the assignment (=).
带有字符串的示例:
a = 'abcd'
b = a
puts a #=> abcd
puts b #=> abcd
a.upcase! # changing a
puts a #=> ABCD
puts b #=> ABCD
a = a.downcase # assigning a
puts a #=> abcd
puts b #=> ABCD
数组示例:
a = [1]
b = a
p a #=> [1]
p b #=> [1]
a << 2 # changing a
p a #=> [1, 2]
p b #=> [1, 2]
a += [3] # assigning a
p a #=> [1, 2, 3]
p b #=> [1, 2]
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