Re: oo design question - how to avoid a factory

Hi, Justin Patrin wrote:

On Fri, 17 Dec 2004 12:39:36 -0500, Andrew Nagy <andrew.nagy@villanova.edu> wrote:

Could using a factory instead of a constructor be confusing to the non-savvy user?

Andrew, a factory isn't confusing by itself. But it is if a new version of Structures_DataGrid requires to use a factory, thus breaking bc. As I stated when I sent this diff to you : "So... It's good we're still in alpha stage because I believe we can't do without a factory." But, still, this "alpha" status is a bit theoritical, because AFAICS, according to pear-general and pear-dev, Structures_DataGrid does have many users. And, for sure, the next release is going to be confusing to all of these, if the factory is required : typing "pear upgrade Structures_DataGrid" will break their software

I don't see a factory as being too confusing, as long as you *always* use the factory in examples and make it clear in the docs that you should (must) use the factory. If you want to avoid the factory you can always make the user call setRenderer() after a 'new' call. Or call it internally whenever you need to use the renderer instead of instantiating it at "new" time.

That's right, I thought about this before coding that factory, but there are many methods in Structures_DataGrid that would need to check if the object is already fully instantiated (bind(), addRecord(), addColumn(), etc...). That would be heavy and dirty. Now, there may be another solution, to keep bc : In the constructor, issue a warning like "Please use the factory...", and then act as a decorator to the real datagrid. This is very possible because the Structures_DataGrid class is currently an almost empty wrapper. Check it out : // Can't extend Structures_DataGrid_Renderer anymore : the decorating // methods would create a conflict with the decorated ones. class Structures_DataGrid {

    var $_decorated;	

    function Structures_DataGrid($limit = null, $page = 1,
                                 $renderer = DATAGRID_RENDER_TABLE)
    {
        PEAR::raiseError("Please use the factory");
        $this->_decorated =& Structures_DataGrid::factory($limit, $page, $renderer);
    }

    function &factory($limit = null, $page=1,$renderer = DATAGRID_RENDER_TABLE)
    {
        // Notice that I instantiate the renderer class directly :

        $dg = new Structures_DataGrid_Renderer($limit, $page);
        $dg->setRenderer($renderer);
        return $dg;
    }

    // Now decorating public methods. These wrappers won't get called by people
    // who used the factory.

    function bind($rs)
    {
         return $this->_decorated->bind($rs);
    }

    function addColumn($column)
    {
         return $this->_decorated->addColumn($column);
    }

    etc....

} One may say that it's heavy, but it's not for the one who directly use the factory. All of this workaround will only create a bit of overhead for people who didn't RTFM recently, but will keep bc. And it could be wiped out in some future major release. What do you all think about this idea ? Is it an acceptable trick ? -- og