constructor methods in interfaces

Question

Are constructor methods in interfaces bad?

Answer 1

First off, I disagree that interface is just a data passing contract. If that were true you would be allowed to define properties in an interface.

I wouldn't exactly think it's weird to do something like:

interface IDBConnection
{
    function __construct( $connectionString );
    function executeNonQuery( $commandText, $paramters=null);
    function executeScalar( $commandText, $paramters=null);
    function executeSingle( $commandText, $paramters=null);
    function executeArray( $commandText, $paramters=null);
}

This would enable you to create instances of third party classes for data access based on simple reflection instead of just being a data contract.

I'm pretty sure that this isn't the best example, I'd go for an abstract base class here in the real world, but I'm also pretty sure that there are perfectly valid reasons for defining a constructor methods' contract in an interface that I haven't thought of.

I haven't seen it done, but i wouldn't think it to be weird or bad.