PHP：如何创建常量的“树”

Question

I wonder if it is possible in PHP to create a "tree" of constants (without instantiating a tree of classes) ... let me explain what I would like to do (code is not correct) :

abstract class logType {
   const Project = 1;
   const User = 2;
}
abstract class dbConstants {
   const logType = logType;
}

So that I use below in my code :

dbConstants::logType::Project

Answer 1

You can only use scalar data (integer, boolean, float and string), with PHP >5.6 you could also use scalar expressions, arrays and resources as the value of a constant as described here . With an array structure you could do something like this then:

abstract class logType
{
    const PROJECT = 1;
    const USER = 2;
}

abstract class dbConstants
{
    const logType = [
        logType::PROJECT,
        logType::USER
    ];
}

echo dbConstants::logType[logType::PROJECT];

Another approach would be to use a trait with public static members like this, if you do not want the class inheritances and reuse your code:

trait logType
{
    public static $PROJECT = 1;
    public static $USER = 2;
}

abstract class dbConstants
{
    use logType;
}

echo dbConstants::$PROJECT;

Another way without the use of an array:

class logType
{
    const PROJECT = 1;
    const USER = 2;
}

abstract class dbConstants
{
    public static $logType;

    public function __construct()
    {
        $this->logType = new logType();
    }
}

echo dbConstants::$logType::PROJECT;

Answer 2

In php 7:

define('animals', [ 'dog', 'cat', 'bird' ]);

This will define a constant array.

In PHP 5.6 you can use const to declare a constant array.

Both of these can contain more arrays to form a structure.