Curly braces in string in PHP

Question

What is the meaning of { } (curly braces) in string literals in PHP?

Answer 1

I've also found it useful to access object attributes where the attribute names vary by some iterator. For example, I have used the pattern below for a set of time periods: hour, day, month.

$periods=array('hour', 'day', 'month');
foreach ($periods as $period)
{
    $this->{'value_'.$period}=1;
}

This same pattern can also be used to access class methods. Just build up the method name in the same manner, using strings and string variables.

You could easily argue to just use an array for the value storage by period. If this application were PHP only, I would agree. I use this pattern when the class attributes map to fields in a database table. While it is possible to store arrays in a database using serialization, it is inefficient, and pointless if the individual fields must be indexed. I often add an array of the field names, keyed by the iterator, for the best of both worlds.

class timevalues
{
                             // Database table values:
    public $value_hour;      // maps to values.value_hour
    public $value_day;       // maps to values.value_day
    public $value_month;     // maps to values.value_month
    public $values=array();

    public function __construct()
    {
        $this->value_hour=0;
        $this->value_day=0;
        $this->value_month=0;
        $this->values=array(
            'hour'=>$this->value_hour,
            'day'=>$this->value_day,
            'month'=>$this->value_month,
        );
    }
}