Can I use a function to return a default param in php?
I would like to do something like this:
function readUser($aUser = loadDefaultUser()){
//doing read User
}
I find that it will display a error to me, how can I pass a function return as a default value? Thank you.
Yes, you can provide a default argument. However, the default argument "must be a constant expression, not (for example) a variable, a class member or a function call."
You can fake this behaviour by using some constant value for the default, then replacing it with the results of a function call when the function is invoked.
We'll use NULL , since that's a pretty typical "no value" value:
function readUser($aUser = NULL) {
if (is_null($aUser))
$aUser = loadDefaultUser();
// ... your code here
}
I would rather give a Null value for this argument and then call loadDefaultUser() in the body of the function. Something like this:
function readUser($aUser = NULL){
if(is_null($aUser)){
$aUser = loadDefaultUser();
}
//...
}
You can add a callback-parameter to your loadDefaultUser() function when it's finished it fires the callback function with the return/result. It's a bit like ajax-javascript callbacks.
function loadDefaultUser ( $callback )
{
$result = true;
return $callback($result);
}
上一篇: 在PHP函数中使用函数结果作为默认参数