blocks|key|1242056|text|在两个单独的语句中进行赋值的问题是，i2+=+i1+%2B+i2将使用i1的新值，而不是正确生成斐波那契序列所需的前一个值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1242057|当您使用并行赋值时，右侧的所有表达式都将首先求值，然后再赋值给左侧的接收变量。|1242058|并行赋值不是一个特殊的运算符。从本质上讲，右边的东西就像一个数组，如果我们在左边列出了多个变量，那么这个数组就会被解包并赋值到各个变量中。|1242059|下面是更多的例子：|1242060|irb(main):020:0>+a+=+1,+2+#+assign+to+a+single+variable
=>+[1,+2]
irb(main):021:0>+a
=>+[1,+2]
irb(main):022:0>+a,+b+=+1,+2+#+unpack+into+separate+variables
=>+[1,+2]
irb(main):023:0>+a
=>+1
irb(main):024:0>+b
=>+2
irb(main):025:0>+a,+b+=+[1,+2,+3]+#+3+is+'lost'+as+no+receiving+variable
=>+[1,+2,+3]
irb(main):026:0>+a
=>+1
irb(main):027:0>+b
=>+2
irb(main):028:0>+first,+*rest+=+[1,+2,+3]+#+*rest+consumes+the+remaining+elements
=>+[1,+2,+3]
irb(main):029:0>+first
=>+1
irb(main):030:0>+rest
=>+[2,+3]|code-block|syntax|javascript|1242061|它是ruby的一个有用的特性，例如，它有助于拥有返回多个值的方法。|1242062|def+sum_and_difference(a,+b)
++a+%2B+b,+a+-+b
end

sum,+difference+=+sum_and_difference+5,+3|1242063|在Java语言中，最接近的方法是返回int[]，但是如果我们想返回一个字符串和一个数字，我们需要创建一个小POJO来充当返回值或返回Object[]的结构，并使用强制转换使代码变得混乱。有关更实际的示例，请参阅我最近回答的this+other+question。|1242064|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/2793495/returning-true-or-error-message-in-ruby/2793517#2793517^0|I|C|X|2|0|0|0|0|0|0|0|I|5|1U|8|33|J|0|0^^$0|@$1|2|3|4|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|19|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|1A|8|@]|D|@]|E|$]]|$1|J|3|K|5|6|7|1B|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1C|8|@]|D|@]|E|$O|P]]|$1|Q|3|R|5|6|7|1D|8|@]|D|@]|E|$]]|$1|S|3|T|5|N|7|1E|8|@]|D|@]|E|$O|P]]|$1|U|3|V|5|6|7|1F|8|@$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]]|D|@$9|1K|A|1L|1|1M]]|E|$]]|$1|W|3|-4|5|6|7|1N|8|@]|D|@]|E|$]]]|X|$Y|$5|Z|10|11|E|$12|13]]]]

The problem with doing the assignment in 2 separate statements is that <code>i2 = i1 + i2</code> will then use the new value of <code>i1</code> rather than the previous value required to correctly generate the Fibonacci sequence.

When you use parallel assignment all of the expressions on the right hand side are evaluated first and then assigned to the receiving variables on the left hand side.

Parallel assignment isn't a special operator. Essentially what is on the right hand side acts as an Array where if we list multiple variables on the left hand side then the array is unpacked and assigned into the respective variables.

Here are some more examples:

<pre><code>irb(main):020:0&gt; a = 1, 2 # assign to a single variable
=&gt; [1, 2]
irb(main):021:0&gt; a
=&gt; [1, 2]
irb(main):022:0&gt; a, b = 1, 2 # unpack into separate variables
=&gt; [1, 2]
irb(main):023:0&gt; a
=&gt; 1
irb(main):024:0&gt; b
=&gt; 2
irb(main):025:0&gt; a, b = [1, 2, 3] # 3 is 'lost' as no receiving variable
=&gt; [1, 2, 3]
irb(main):026:0&gt; a
=&gt; 1
irb(main):027:0&gt; b
=&gt; 2
irb(main):028:0&gt; first, *rest = [1, 2, 3] # *rest consumes the remaining elements
=&gt; [1, 2, 3]
irb(main):029:0&gt; first
=&gt; 1
irb(main):030:0&gt; rest
=&gt; [2, 3]
</code></pre>

It is a useful feature of ruby, for example it facilitates having methods that return multiple values e.g.

<pre><code>def sum_and_difference(a, b)
 a + b, a - b
end

sum, difference = sum_and_difference 5, 3
</code></pre>

In Java the closest thing would be to have a method that returned <code>int[]</code> but if we wanted to return a string and a number we'd need to create a little POJO to act as struct for the return value or return <code>Object[]</code> and clutter the code up with casts. See <a href="https://stackoverflow.com/questions/2793495/returning-true-or-error-message-in-ruby/2793517#2793517">this other question</a> that I answered recently for a more practical example.

blocks|key|1027277|text|我正在读同样的东西，也有同样的问题。如果它是这样写的，就不会那么令人困惑，也会更有意义：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1027278|def+fib_up_to(max)
++i1+=+i2+=+1
++while+i1+<=+max
++++yield+i1
++++i1,+i2+=+i2,+i1%2Bi2
++end
end

fib_up_to(100)+{%7Cf%7C+print+f,+"+"+}|code-block|syntax|javascript|1027279|在我看来，使用i1,+i2+=+1,+1是没有意义的。但是这种类型的赋值对于第5行来说是有意义的。|offset|length|style|CODE|1027280|entityMap^0|0|0|7|D|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I was reading the same thing and had the same question. It would be less confusing and make more sense if it had been written like this:

<pre><code>def fib_up_to(max)
 i1 = i2 = 1
 while i1 &lt;= max
 yield i1
 i1, i2 = i2, i1+i2
 end
end

fib_up_to(100) {|f| print f, " " }
</code></pre>

Using <code>i1, i2 = 1, 1</code> doesn't make sense in my opinion. But that type of assignment does makes sense for line 5.

I was going through an example from the Programming in Ruby book:

<pre><code>def fib_up_to(max)
 i1, i2 = 1, 1 # parallel assignment (i1 = 1 and i2 = 1)
 while i1 &lt;= max
 yield i1
 i1, i2 = i2, i1+i2
 end
end
fib_up_to(100) {|f| print f, " " }
</code></pre>

This simply prints the Fibonacci numbers up to 100. That's fine. When I replace the parallel assignment with:

<pre><code>i1 = i2
i2 = i1+i2
</code></pre>

I am not getting the desired output. 

Is it advisable to use parallel assignments? I come from a Java background and it feels really weird to see this type of assignment.

One more question is: Is parallel assignment an operator?

Parallel Assignment operator in Ruby

Java

我正在学习Ruby中的一个例子：def fib_up_to(max) i1, i2 = 1, 1 # parallel assignment (i1 = 1 and i2 = 1) while i1 <= max yield i1 i1, i2 = i2, i1+i2 endendfib_up_to(...

问Ruby中的并行赋值运算符
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Ruby中的并行赋值运算符EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Ruby中的并行赋值运算符
EN