范围:本地与 Var [英] Scoping: Local vs Var

问题描述

我是 CF 新手，所以这可能是一个基本问题.但是我听说由于 CF 中的作用域如何工作，我应该将 local 用于函数内部的对象.但是'var'呢?var 和使用 local 一样吗?

I'm new to CF so this may be a basic question. But I've heard I should use local for objects inside functions due to how scoping works in CF. But what about 'var'? Is var the same as using local?

例如

function MyFunction()
{
    local.obj = {};
}

这是否与:

function MyFunction()
{
    var obj = {};
}

如果它们不一样，它们之间有什么区别?我应该什么时候使用它们中的任何一个?

If they aren't the same, what is the difference between them? And when should I be using either of them?

推荐答案

它们非常相似，但并不完全相同.两者都只存在于函数内部，但它们的工作方式略有不同.

They are very similar, but not exactly the same. Both only exist inside of a function but they work slightly differently.

var 版本通过所有默认变量范围工作.请参阅 http://help.adobe.com/en_US/ColdFusion/9.0/Developing/WSc3ff6d0ea77859461172e0811cbec09af4-7fdf.html

The var version works it way through all the default variable scopes. See http://help.adobe.com/en_US/ColdFusion/9.0/Developing/WSc3ff6d0ea77859461172e0811cbec09af4-7fdf.html

Local 将仅匹配本地范围内的变量.考虑以下

Local will match only a variable in a local scope. Consider the following

<cffunction name="himom">
    <cfoutput>
        <p><b>try 0:</b> #request_method#</p>
        <!--- you might think that the variable does not exist, 
              but it does because it came from cgi scope --->
    </cfoutput> 

    <cfquery name="myData" datasource="Scorecard3">
        SELECT 'This is via query' AS request_method
    </cfquery>
    <!--- Data is now being loaded into a query --->

    <cfoutput query="myData">
        <p><b>try 1:</b> #request_method#</p>
    </cfoutput>
    <!--- This one now came from the query --->        

    <cfset var request_method = "This is Var">
    <!--- We now declare via var ---> 
 
    <cfoutput query="myData">
        <p><b>try 2:</b> #request_method#</p>
    </cfoutput> 
    <!--- the query version disappears and now 
          the var version takes precedence --->

    <cfset local.request_method = "This is local">
    <!--- now we declare via local --->

    <cfoutput query="myData">
        <p><b>try 3:</b> #request_method#</p>
    </cfoutput>
    <!--- The local method takes precedence --->

    <cfoutput>
        <p><b>try 4:</b> #request_method#</p>
        <!--- in fact it even takes precedence over the var --->

        <p><b>try 5:</b> #local.request_method#</p>
        <!--- there is no question where this comes from --->   
   </cfoutput>
</cffunction>

<cfset himom()>

以上结果

尝试 0:获取

尝试 1:这是通过查询

try 1: This is via query

尝试 2:这是 Var

try 2: This is Var

尝试 3:这是本地的

尝试 4:这是本地的

尝试 5:这是本地的

总结

在开发时，您可以使用其中任何一种来确保变量只存在于函数内部，但始终在变量前加上 local 可以确保您的代码被清楚地理解

When developing, you could use either to make sure that variables only exist inside of a function, but always prefixing your variables with local goes a long way in making sure that your code is clearly understood

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