Wednesday, October 21, 2009

Laws of dependency injection

As a heavy user of dependency injection, I’m always careful when applying it. “If you have a hammer, everything looks like a nail.”  Nikola Malovic mentions on his blog the following laws about the usage of an IOC container.

Nikola’s 5 laws of IoC:

  1. “Store in IoC container only services. Do not store any entities.”
  2. "Any class having more then 3 dependencies should be questioned for SRP violation"
  3. “Every dependency of the class has to be presented in a transparent manner in a class constructor.”
  4. “Every constructor of a class being resolved should not have any implementation other then accepting a set of its own dependencies.”
  5. “IoC container should be explicitly used only in Bootstrapper. Any other “IoC enabled” code (including the unit tests) should be completely agnostic about the existence of IoC container."

Although I don’t agree with all of his laws, he makes some good points.

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