我可以在PHP中使用类属性设置默认方法参数吗? [英] Can I set up a default method argument with class property in PHP?

问题描述

我正在使用PHP 5.2.6.我想为方法中的参数提供默认值，但看来我有点太聪明了.

I'm using PHP 5.2.6. I want to have a default value for an argument in a method, but it seems I'm getting a bit too clever.

类属性blnOverwrite是默认的，并且可以在该类的其他地方设置.我有一个方法想要再次设置它，但不覆盖现有值.尝试此操作时出现错误:

The class property blnOverwrite is defaulted and settable elsewhere in the class. I have a method where I want to have it settable again, but not override the existing value. I get an error when I try this:

public function place( $path, $overwrite = $this->blnOverwrite ) { ... }

我必须做这样的事情吗?

Must I do something like this?

public function place( $path, $overwrite = NULL ) { 
    if ( ! is_null($overwrite) ) {
        $this->blnOverwrite = $overwrite;
    }
    ...
}

推荐答案

是的，您必须这样做.您不能将成员值用作默认参数值.

Yes, you have to do it this way. You cannot use a member value for the default argument value.

摘自PHP手册中有关函数参数的内容:(强调我的)

一个函数可以为标量参数定义C ++风格的默认值. […] PHP还允许使用数组和特殊类型NULL作为默认值. […] 默认值必须是一个常量表达式，而不是(例如)变量，类成员或函数调用. […]请注意，使用默认参数时，任何默认值都应为on任何非默认参数的右侧；否则，事情将无法按预期进行.

A function may define C++-style default values for scalar arguments. […] PHP also allows the use of arrays and the special type NULL as default values. […] The default value must be a constant expression, not (for example) a variable, a class member or a function call. […] Note that when using default arguments, any defaults should be on the right side of any non-default arguments; otherwise, things will not work as expected.

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