Use private var in declaration of other private var in php

问题

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";
}

But this ends in a PHP Fatal error: Constant expression contains invalid operations

Tried it with and withoud $this->

Is there a way to do this in php?

回答1:

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

Constant expressions

Constants can be used in default values:

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

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

Initialising in the constructor

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";
    }
}

来源：https://stackoverflow.com/questions/40185018/use-private-var-in-declaration-of-other-private-var-in-php