Home / Questions / 431068
Accepted
ArcanisGK507
Asked: 2022-02-26 09:16:01 +0800 CST 2022-02-26 09:16:01 +0800 CST

use class property as default value

  • 772

I have a class and in the constructor I determine the value of a property of the class; Why can't I use this class property as a default value in a method?

Or am I not using the proper property or property type?

class FooClass
{
    public string $defenv = '';
    public function __construct($theme = 'default')
    {
        //En el constructor determino el tipo de interface usada
        $this->defenv = $this->IsCommandLineInterface() ? 'cli' : 'web';
    }
    private function IsCommandLineInterface()
    {
        return (php_sapi_name() === 'cli');
    }
    public function foo($env = $this->defenv){
        echo $env;
    }
}

Mistake

Fatal error: Constant expression contains invalid operations in

I find myself needing to make these changes to make it work (it's still inside the class):

public function foo($env = ''){
    if ($env == '') {
        $env = $this->defenv;
    }
    echo $env;
}

Note: I have previously instantiated the class and call it as follows:

$example = new FooClass();
$example->foo()
php

2 Answers

  1. Best Answer

    The particular case you want to solve can be achieved. But, generating the constant to be used by using the define() method that supports the use of functions that return some value as values ​​to assign.
    The solution could look like this:

    <?php
\**
 * @filename: FooClass.php
 */
define('ENTORNO', IdentificarEntorno() ); 

class FooClass
{
    public string $defenv = '';
    public function __construct($theme = 'default')
    {
        //En principio no se necesitaría asignar la propiedad a no ser
        //que se espere que la usen clases derivadas de ella.
        // la asigno para mantenerla.
        // Podría haberse asignado directamente en la declaración y
        //es redundante con la constante declarada.
        $this->defenv = ENTORNO;
    }
    
    public function foo($env = ENTORNO){
        echo $env;
    }
}

function IdentificarEntorno()
{
    return (php_sapi_name() === 'cli') ? 'cli' : 'web';
}
    • 3

  2. In the documentation for in the Default Argument ValuesPHP ​​section it says:

    The default value must be a constant expression, not (for example) a variable, a class member, or a function call.

    One solution ( as @Triby commented ) is to use the null merge operator

    Example:

    public function foo($env = null){
    echo $env ?? $this->defenv;
}
    • 2