blocks|key|3749950|text|在第二条语句中，编译器必须决定他必须使用哪种类型。也就是说，5是一个整数，他也可以假设你的意思是|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3749951|var+a:int+=+5;++or++var+a:uint+=+5;|code-block|syntax|javascript|3749952|另外，为了代码完成的目的，最好定义一个类型;-)但这并不是一个真正的理由，因为一些IDE也可以处理这些类型。|3749953|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

in the 2nd statement the compiler has to decide which type he has to use. 
i.e 5 is an integer he also could assume you mean 

<pre><code>var a:int = 5; or var a:uint = 5;
</code></pre>

also for code completion purposes it's better do define a type ;-) but that's not a real reason to do, because some IDE's can handle these too.

blocks|key|1434569|text|在像AS3这样具有强静态类型的语言中，你应该总是在解密时输入你的对象，这将使你的代码更干净，并帮助你更容易地追踪错误。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1434570|也就是说，AS3通常是非常宽容的，并且能够在运行时确定您需要哪种类型。例如，下面的代码片段运行良好：|1434571|++++private+var+foo;

++++public+final+function+run():void+{

++++++++bar();
++++++++baz();
++++}

++++private+function+bar():void+{

++++++++foo+=+4;
++++++++foo+-=+0.5;
++++++++trace(+foo+);+//+traces+"3.5"
++++}

++++private+function+baz():void+{

++++++++foo+=+"qux";
++++++++trace(+foo+);+//+traces+"qux"
++++}|code-block|syntax|javascript|1434572|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|M|8|@]|9|@]|A|$G|H]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

In a language with strong static typing like AS3 you should always be typing your objects at decleration, it will make your code cleaner and help you track down bugs easier.

That said, AS3 is usually quite forgiving and is able to figure out which type you need at runtime. For example, this snippet works fine:

<pre><code> private var foo;

 public final function run():void {

 bar();
 baz();
 }

 private function bar():void {

 foo = 4;
 foo -= 0.5;
 trace( foo ); // traces "3.5"
 }

 private function baz():void {

 foo = "qux";
 trace( foo ); // traces "qux"
 }
</code></pre>

blocks|key|3750030|text|总是定义一个类型。如前所述，如果您不这样做，编译器将为您选择，并且可能不会像预期的那样。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3750031|在处理类时，它也变得很重要。例如，您在类中创建一个私有变量foo，例如：|offset|length|style|CODE|3750032|private+var+_foo;+//+no+type+is+defined|code-block|syntax|javascript|3750033|稍后，您需要为它添加一个get/set属性：|3750034|public+function+get+foo():???+{+return+_foo;+}
public+function+set+foo(val:???):void+{+_foo+=+val;+}|3750035|你会传递什么？您如何将其记录下来以供其他人使用？|3750036|就好像你有|3750037|private+var+_foo:Number;

public+function+get+foo():Number+{+return+_foo;+}
public+function+set+foo(val:Number):void+{+_foo+=+val;+}|3750038|很明显，foo在get/set两种情况下都做了什么。|3750039|还有一件事。如果要创建引用舞台上的内容的MovieClip变量，请这样做：|3750040|var+mymc+=+stage_mc;+//+Hmmm,+not+so+good|3750041|如果你想在mymc上调用一个MovieClip方法，比如play()，编译器会抛出一个错误，因为它不“知道”mymc有一个play方法(怎么会呢？)因此，通过键入它(在向其添加类型的意义上，如MovieClip)，您可以让编译器知道哪些方法和属性应该是可用的。|3750042|示例：|3750043|var+mymc:MovieClip+=+stage_mc;+//+Ahh,+much+better!|3750044|它还允许编译器进行类型检查。因此，在上面的示例中，如果您试图将文本字段传递给movieclip变量mymc，则会抛出一个错误。这可以阻止更大的bug潜入。|3750045|我对AS3中的类型检查非常感兴趣--我很高兴Flash最终引入了它，现在它已经出现了，让我们使用它吧！|3750046|entityMap^0|0|T|3|0|0|0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1F|8|@$D|1G|E|1H|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1J|8|@]|9|@]|A|$]]|$1|O|3|P|5|J|7|1K|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1L|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1M|8|@]|9|@]|A|$]]|$1|U|3|V|5|J|7|1N|8|@]|9|@]|A|$K|L]]|$1|W|3|X|5|6|7|1O|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|6|7|1P|8|@]|9|@]|A|$]]|$1|10|3|11|5|J|7|1Q|8|@]|9|@]|A|$K|L]]|$1|12|3|13|5|6|7|1R|8|@]|9|@]|A|$]]|$1|14|3|15|5|6|7|1S|8|@]|9|@]|A|$]]|$1|16|3|17|5|J|7|1T|8|@]|9|@]|A|$K|L]]|$1|18|3|19|5|6|7|1U|8|@]|9|@]|A|$]]|$1|1A|3|1B|5|6|7|1V|8|@]|9|@]|A|$]]|$1|1C|3|-4|5|6|7|1W|8|@]|9|@]|A|$]]]|1D|$]]

Always define a type. As mentioned, if you don't the compiler will choose for you, and it may not be as expected. 

It also becomes important when dealing with classes. For example you create a private variable <code>foo</code> in your class, such as:

<pre><code>private var _foo; // no type is defined
</code></pre>

Later down the track, you want to add a get/set property for it:

<pre><code>public function get foo():??? { return _foo; }
public function set foo(val:???):void { _foo = val; }
</code></pre>

What would you be passing in? And how do you document this for someone else to use? 

Where as if you had 

<pre><code>private var _foo:Number;

public function get foo():Number { return _foo; }
public function set foo(val:Number):void { _foo = val; }
</code></pre>

It is clear, straight away what foo does in both the get/set cases.

And one more thing. If you want to create a MovieClip variable which references something on the stage, say:

<pre><code>var mymc = stage_mc; // Hmmm, not so good
</code></pre>

If you wanted to call a MovieClip method on mymc, say play(), the compiler will throw an error because it doesn't 'know' mymc has a play method (how would it?). So by typing it (in the sense of adding a type to it, like MovieClip), you are letting the compiler know what methods and properties should be available. 

Example:

<pre><code>var mymc:MovieClip = stage_mc; // Ahh, much better!
</code></pre>

It also alows the compiler to do type checking. So in the above example, if you tried to pass in a textfield to the movieclip variable mymc, an error will throw an error. This stops bigger bugs sneaking in. 

I'm very passionate about type checking in AS3 - I'm glad Flash finally introduced it, and now that it's here, let's use it!

blocks|key|1313296|text|还要考虑优化。即使你可以声明你的变量没有类型，比如|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1313297|var+a:*+=+5，什么可以用的很棒，还是考虑下面的优化测试：|offset|length|style|CODE|1313298|var+a+=+5;
var+b:*+=+5;
var+c:Number+=+5;
var+d:int+=+5;
var+e:uint+=+5;

var+time_start:Number+=+getTimer();

for(var+i:int+=+0;+i+<+10000000;+i%2B%2B)
{
++++a+%2B=+1;
++++//b+%2B=+1;
++++//c+%2B=+1;
++++//d+%2B=+1;
++++//e+%2B=+1;
}

var+time_stop:Number+=+getTimer();

trace(time_stop+-+time_start,+"ms");

//a.)+650+ms
//b.)+651+ms
//c.)+106+ms
//d.)+69+ms
//e.)+69+ms|code-block|syntax|javascript|1313299|结果显示了每轮在一台普通机器上的表现。无论上面示例中的确切数字是什么，重点都是查看速率：|1313300|在a和b的情况下，我们没有给变量指定类型。在第三种情况下(c.)我们给了它一个类型，我们达到了6.14倍的速度提升。|BOLD|1313301|在d和e的情况下，您可以看到如果您确实专门设置了类型会发生什么:整型和无符号整型。这种情况下，如果你使用整数，你能获得的速度是非常大的(10x)。|1313302|在编写随机函数、大型计算或复杂引擎时，请考虑这一点。|1313303|entityMap^0|0|0|B|0|0|0|1B|B|0|0|21|0|0|Q|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Y|8|@$D|Z|E|10|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|11|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|12|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|13|8|@$D|14|E|15|F|Q]]|9|@]|A|$]]|$1|R|3|S|5|6|7|16|8|@$D|17|E|18|F|Q]]|9|@]|A|$]]|$1|T|3|U|5|6|7|19|8|@$D|1A|E|1B|F|Q]]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]]|W|$]]

Also think about optimization. Even though you can declare your variable with no type, like

<code>var a:* = 5</code>, what can be used awesomely, still consider the following optimization test:

<pre><code>var a = 5;
var b:* = 5;
var c:Number = 5;
var d:int = 5;
var e:uint = 5;

var time_start:Number = getTimer();

for(var i:int = 0; i &lt; 10000000; i++)
{
 a += 1;
 //b += 1;
 //c += 1;
 //d += 1;
 //e += 1;
}

var time_stop:Number = getTimer();

trace(time_stop - time_start, "ms");

//a.) 650 ms
//b.) 651 ms
//c.) 106 ms
//d.) 69 ms
//e.) 69 ms
</code></pre>

The results show each round on an average machine. Whatever the numbers are exactly in the example above, the point is to see the rate:

In cases a and b, we didn't give a type to the variable. In the third case (c.) we gave it a type, and we reached a 6.14 times speed increase.

In cases d and e, you can see what happens if you really set the type specifically: integer and unsigned integers. This case, so if you use integers, the speed you can gain is really big (10x).

Think about this when writing random functions, big calculations or complex engines.

blocks|key|1434684|text|在AS3中，几乎没有什么理由不显式地键入某些内容。在某些情况下，它是适当的，但类型系统是为了防止出现问题。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1434685|至于速度/内存差异，这是一个很好的解释：http://onflex.org/ACDS/AS3TuningInsideAVM2JIT.pdf|offset|length|1434686|entityMap|0|LINK|mutability|MUTABLE|url|http://onflex.org/ACDS/AS3TuningInsideAVM2JIT.pdf^0|0|K|1D|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

In AS3 there is nearly no good reason to not explicitly type something. There are cases when it is appropriate, but the type system is there to prevent problems.

As for speed / memory differences, this is a pretty good explanation: <a href="http://onflex.org/ACDS/AS3TuningInsideAVM2JIT.pdf" rel="nofollow">http://onflex.org/ACDS/AS3TuningInsideAVM2JIT.pdf</a>

Last night I thought about this question in Flash

<pre><code>var a:Number = 5;
var a = 5;
</code></pre>

What declaration is better? Does first declaration work faster and take less memory?
All examples of AS contain first declaration method(e.g. <a href="http://actionscriptexamples.com/2010/05/03/getting-started-with-the-tlftextfield-class-in-actionscript-3-0-and-flash-cs5/" rel="nofollow">http://actionscriptexamples.com/2010/05/03/getting-started-with-the-tlftextfield-class-in-actionscript-3-0-and-flash-cs5/</a>).

<pre><code>var tlfTxt:TLFTextField = new TLFTextField();
</code></pre>

Why do they use first method instead of second?

var a:Number = 5 vs var a=5 (ActionScript)

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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昨晚我在Flash上思考了这个问题var a:Number = 5;var a = 5;哪个声明更好？第一个声明是否工作得更快，占用的内存更少？AS的所有示例都包含第一个声明方法(例如)。var tlfTxt:TLFTextField = new TLFTextField();为什么他们使用第一种方法而不是第二种方法？

问var a:数字=5与var a=5 (ActionScript)
EN

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问var a:数字=5与var a=5 (ActionScript)EN