将变量作为参数默认值的 PHP 函数
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PHP function with variable as default value for a parameter
提问by The Bndr
By default a PHP function uses $_GETvariables. Sometimes this function should be called in an situation where $_GETis not set. In this case I will define the needed variables as parameter like: actionOne(234)
默认情况下，PHP 函数使用$_GET变量。有时应该在$_GET未设置的情况下调用此函数。在这种情况下，我将所需的变量定义为参数，如：actionOne(234)
To get an abstract code I tried something like this:
为了得到一个抽象代码，我尝试了这样的事情：
function actionOne($id=$_GET["ID"])
which results in an error:
这导致错误：
Parse error: syntax error, unexpected T_VARIABLE
解析错误：语法错误，意外的 T_VARIABLE
Is it impossible to define an default parameter by using an variable?
使用变量定义默认参数是不可能的？
Edit
编辑
The actionOneis called "directly" from an URL using the framework Yii. By handling the $_GETvariables outside this function, I had to do this on an central component (even it is a simple, insignificant function) or I have to change the framework, what I don't like to do.
在actionOne从一个URL使用该框架被称为“直接”的Yii。通过处理$_GET这个函数之外的变量，我不得不在一个中心组件上做这件事（即使它是一个简单的、无关紧要的函数），或者我必须改变框架，这是我不喜欢做的。
An other way to do this could be an dummy function (something like an pre-function), which is called by the URL. This "dummy" function handles the variable-issue and calls the actionOne($id).
执行此操作的另一种方法可能是由 URL 调用的虚拟函数（类似于前置函数）。这个“虚拟”函数处理变量问题并调用actionOne($id).
回答by John Parker
No, this isn't possible, as stated on the Function arguments manual page:
不，这是不可能的，如函数参数手册页所述：
The default value must be a constant expression, not (for example) a variable, a class member or a function call.
默认值必须是常量表达式，而不是（例如）变量、类成员或函数调用。
Instead you could either simply pass in null as the default and update this within your function...
相反，您可以简单地传入 null 作为默认值并在您的函数中更新它...
function actionOne($id=null) {
$id = isset($id) ? $id : $_GET['ID'];
....
}
...or (better still), simply provide $_GET['ID'] as the argument value when you don't have a specific ID to pass in. (i.e.: Handle this outside the function.)
...或者（更好），当您没有要传入的特定 ID 时，只需提供 $_GET['ID'] 作为参数值。（即：在函数外部处理。）
回答by Galen
function actionOne( $id=null ) {
if ($id === null) $id = $_GET['ID'];
}
But, i would probably do this outside of the function:
但是，我可能会在函数之外执行此操作：
// This line would change, its just a for instance
$id = $id ? $id : $_GET['id'];
actionOne( $id );
回答by markus
You should get that id before you call the function. Checking for the existence of the parameter breaks encapsulation. You should do something like that:
您应该在调用该函数之前获得该 ID。检查参数是否存在会破坏封装。你应该做这样的事情：
if (isset($_GET["ID"])
{
$id = $_GET["ID"];
}
else
{
//$id = something else
}
function doSomethingWithID($id)
{
//do something
}
回答by Naftali aka Neal
Yes it is impossible.
是的，这是不可能的。
The default has to be a static variable:
默认值必须是静态变量：
function actionOne( $id='something') {
//code
}
回答by Mihail Gershkovich
Easy peanuts!
(Might contain minor mistakes, errors or typos!)
简单的花生！
（可能包含小错误、错误或错别字！）
You need a helper function, which will call you main function recursively, but having NULL as default:
您需要一个辅助函数，它将递归调用您的主函数，但默认值为 NULL：
Wrong: function actionOne($id=$_GET["ID"])
错误的： function actionOne($id=$_GET["ID"])
Right:
对：
function actionOne($id) {...}
function actionOnewithID($id=NULL) {
if (NULL==$id){actionOne($_GET["ID"]);}
else {actionOne($id);
}
And if you need to return a value:
如果您需要返回一个值：
function actionOne($id) {...}
function actionOnewithID($id=NULL) {
if (NULL==$id){return(actionOne($_GET["ID"]));}
else {return(actionOne($id));
}
I hope this helps!
我希望这有帮助！
回答by pablo henrique
You could use constant variable
你可以使用常量变量
define('ID',$_GET["ID"]);
function($id = _ID_){
//code
}
