Question

starting use oop

why:

class user 
{
    private $pdo;

    function __construct()
    {
        $this->pdo = singleton::get_instance()->PDO_connection();
    }

...
}

this works fine. but this:

class user 
{
    private $pdo = singleton::get_instance()->PDO_connection();

...
}

this does not working. Error parse error, expecting ','' or ';'' in ...

what is wrong with second variant?

Answer 1

See the last sentence of the first paragraph of Properties in the PHP OOP documentation:

Class member variables are called
“properties”. You may also see them
referred to using other terms such as
“attributes” or “fields”, but for the
purposes of this reference we will use
“properties”. They are defined by
using one of the keywords public,
protected, or private, followed by a
normal variable declaration. This
declaration may include an
initialization, but this
initialization must be a constant
value–that is, it must be able to be
evaluated at compile time and must not
depend on run-time information in
order to be evaluated.

In other words, the database handler returned by this statement is not a constant value and therefore will not be available at compile time:

singleton::get_instance()->PDO_connection();