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Ruby变量(数组)赋值错误(使用push方法)

ruby

2

fflyer05 · 技术社区 · 15 年前

#!/usr/bin/ruby -w
@instance_ar = [1,2,3,4]
local_ar = @instance_ar
local_ar_2 = local_ar
###
irrelevant_local_ar = [5,6,7,8]
###
for i in irrelevant_local_ar
    local_ar_2.push(i)
end
count = 0
for i in local_ar_2
    puts "local_ar_2 value: #{i} and local_ar value: #{local_ar[count]} and @instance_ar value: #{@instance_ar[count]}\n"
    count += 1
end

它的输出是

local_ar_2 value: 1 and local_ar value: 1 and @instance_ar value: 1
local_ar_2 value: 2 and local_ar value: 2 and @instance_ar value: 2
local_ar_2 value: 3 and local_ar value: 3 and @instance_ar value: 3
local_ar_2 value: 4 and local_ar value: 4 and @instance_ar value: 4
local_ar_2 value: 5 and local_ar value: 5 and @instance_ar value: 5
local_ar_2 value: 6 and local_ar value: 6 and @instance_ar value: 6
local_ar_2 value: 7 and local_ar value: 7 and @instance_ar value: 7
local_ar_2 value: 8 and local_ar value: 8 and @instance_ar value: 8

push 到 local_ar_2 更改其他两个数组?我对局部变量的理解是,一旦它们被创建,它们就不应该影响任何其他变量,因为它们是局部的。

来自C和Perl,这让我大吃一惊。

2 回复 | 直到 15 年前

1

9

Peter Mortensen Pieter Jan Bonestroo 15 年前

Ruby与引用一起工作!记住这一点。如果你想要一份拷贝,你必须这样做:

@instance_ar = [1,2,3,4]
local_ar = @instance_ar.clone
local_ar_2 = local_ar.clone

编辑:

a = ["a", "b", "c"]
b = a[0]
b = "d" # We assign a new object to b!

a 是:

但是:

a = ["a", "b", "c"]
b = a[0]
b[0] = "d" # We are working with the reference!

a is:
=> ["d", "b", "c"]

a = "hello"
b = a
b += " world" 
# Is the same as b = b + " world", we assign a new object!

是: =>“你好”

a = "hello"
b = a
b<<" world"
# We are working with the reference!

a = "abc"
b = a
b[0] = "d" # we are working with the reference

是: =>“dbc”

http://ruby-doc.org/docs/ProgrammingRuby/ . 向下滚动到几乎在页面底部的“变量”。

2

3

Mladen JablanoviÄ 15 年前

在Ruby中,您并不“创建变量”,而是创建对象(在您的例子中是数组),并将它们分配给变量。所以,在你的例子中,你有一个有两个名字的数组, local_ar 和 local_ar_2 . 之后你改变了对象,而不是变量(它们仍然指向同一个被改变的对象)。

你说你来自C,看看这个例子:

int a[5];
int * b;

a[0] = 10;
a[1] = 20;
b = a;
b[1] = 5;

printf("%d", a[1]);

打印什么号码?这与Ruby代码中发生的情况几乎相同。

for 因为遍历数组在Ruby中不是惯用的。通常使用:

local_ar_2.each_with_index do |i, count|
    puts "local_ar_2 value: #{i} and local_ar value: #{local_ar[count]} and @instance_ar value: #{@instance_ar[count]}\n"
end