5.3. Constrained Construction

The biggest challenge of properly implementing DI is getting all classes with DEPENDENCIES moved to a COMPOSITION ROOT. When we accomplish this, we’ve already come a long way.

Even so, there are still some traps to look out for. A common mistake is to require all DEPENDENCIES to have a constructor with a particular signature. This normally originates from the desire to attain late binding so that DEPENDENCIES can be defined in an external configuration file and thereby changed without recompiling the application.