Question

For example I have this in a class:

private $messages = array( 
    'name'=>        '<aa_f>name',
    'PASS' =>       '<aa_p>'
);

but I want to make <aa_p> a variable like this:

private $pass = '<aa_p>';

I’ve tried these 4 ways and none work. PHP.net had no example of doing this.

    'PASS' =>       $this->pass
    'PASS' =>       $pass
    'PASS' =>       '$this->pass'
    'PASS' =>       '$pass'

Full Code

<?php
class Message
{
    private $PASS = '<aa_p>';
    private $FAIL = '<aa_f>';

    private $messages = array( 
        'name'=>        '<aa_f>name',
        'email' =>      '<aa_f>email_s', 
        'pass' =>       '<aa_f>pass',
        'url' =>        '<aa_f>url',
        'title' =>      '<aa_f>title',
        'tweet'=>       '<aa_f>tweet',
        'empty' =>      '<aa_f>empty', 
        'same' =>       '<aa_f>same',  
        'taken' =>      '<aa_f>taken', 
        'validate' =>   '<aa_f>validate',
        'PASS' =>       '<aa_p>'
    );
    public function __construct()
    {
    }
    public function display($type)
    {
        echo $this->messages[$type];
    }
    public function get($type)
    {
        return $this->messages[$type];
    }
}

Update : Answer

For Reference: ( Updated Code )

class Message
{
    private $PASS = '<aa_p';
    private $FAIL = '<aa_f>';
    private $messages = array();

    public function __construct()
    {
        $this->messages['PASS'] = $this->PASS;
        $this->messages['name'] = $this->FAIL . 'name';
        $this->messages['email'] = $this->FAIL . 'email_s';
        $this->messages['pass'] = $this->FAIL . 'pass';
        $this->messages['url'] = $this->FAIL . 'url';
        $this->messages['title'] = $this->FAIL . 'title';
        $this->messages['tweet'] = $this->FAIL . 'tweet';
        $this->messages['empty'] = $this->FAIL . 'empty';
        $this->messages['same'] = $this->FAIL . 'same';
        $this->messages['taken'] = $this->FAIL . 'taken';
        $this->messages['validate'] = $this->FAIL . 'validate';
    }
    public function display($type)
    {
        echo $this->messages[$type];
    }
    public function get($type)
    {
        return $this->messages[$type];
    }
}

Answer 1

Only values that can be determined at compile time may be used to initiate class members. You will need to set the value at run-time (through the constructor):

class Message
{
    private $PASS = '<aa_p';
    private $FAIL = '<aa_f>';

    private $messages = array( 
        'name'=>        '<aa_f>name',
        'email' =>      '<aa_f>email_s', 
        'pass' =>       '<aa_f>pass',
        'url' =>        '<aa_f>url',
        'title' =>      '<aa_f>title',
        'tweet'=>       '<aa_f>tweet',
        'empty' =>      '<aa_f>empty', 
        'same' =>       '<aa_f>same',  
        'taken' =>      '<aa_f>taken', 
        'validate' =>   '<aa_f>validate',
        'PASS' =>       null
    );


    public function __construct()
    {
        $this->messages['PASS'] = $this->PASS;
    }

}