在php中其他private var的声明中使用private var [英] Use private var in declaration of other private var in php

问题描述

是否可以使用私有变量声明另一个私有变量?我的代码如下:

Is there a way to use a private variable to declare an other private variable? My Code looks like this:

class MyClass{
    private $myVar = "someText";
    private $myOtherVar = "something" . $this->myVar . "else";
}

但这以PHP Fatal error: Constant expression contains invalid operations

与$this->一起尝试过

有没有办法在php中做到这一点?

Is there a way to do this in php?

推荐答案

属性的默认值在编译时不能基于其他属性.但是，有两种选择.

Default values for properties can't be based on other properties at compile-time. However, there are two alternatives.

常量可以使用默认值:

class MyClass {
    const MY_CONST = "someText";
    private $myVar = self::MY_CONST;
    private $myOtherVar = "something" . self::MY_CONST . "else";
}

从PHP 7.1开始，这样的常数本身可以是私有的(private const).

As of PHP 7.1, such a constant could itself be private (private const).

可以声明没有默认值的属性，并在类的构造函数中为其赋值:

Properties can be declared with no default value, and assigned a value in the class's constructor:

class MyClass {
    private $myVar = "someText";
    private $myOtherVar;

    public function __construct() {
        $this->myOtherVar = "something" . $this->myVar . "else";
    }
}

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