抽象类的属性可以在类外访问吗？

Question

Is is possible to access a variable in a PHP abstract class, i.e.

abstract class Settings
{
    public $application = array
    (
        'Name' => 'MyApp',
        'Version' => '1.0.0',
        'Date' => 'June 1, 2017'
    )
}

echo Settings::application ['Name'];   // doesn't work

Answer 1

You could make the variable static, as long as it doesn't need to allow differentiation across instances (i.e. instance variable):

<?php
// example code

abstract class Settings
{
    public static $application = array
    (
        'Name' => 'MyApp',
        'Version' => '1.0.0',
        'Date' => 'June 1, 2017'
    );
}

echo Settings::$application ['Name'];

Run it in this playground example.

Though your original access of application was similar to that of a constant. use const to declare a Class constant:

abstract class Settings
{
    const application = array
    (
        'Name' => 'MyApp',
        'Version' => '1.0.0',
        'Date' => 'June 1, 2017'
    );
}

echo Settings::application ['Name'];

Run it in this playground example.