oop - How much work should be done in a constructor?

Question

Should operations that could take some time be performed in a constructor or should the object be constructed and then initialised later.

For example when constructing an object that represents a directory structure should the population of the object and its children be done in the constructor. Clearly, a directory can contain directories and which in turn can contain directories and so on.

What is the elegant solution to this?

Answer 1

To summarize:

• At a minimum, your constructor needs to get the object configured to the point that its invariants are true.

• Your choice of invariants may affect your clients.(Does the object promise to be ready for access at all times? Or only only in certain states?) A constructor that takes care of all of the set-up up-front may make life simpler for the class's clients.

• Long-running constructors are not inherently bad, but may be bad in some contexts.

• For systems involving a user-interaction, long-running methods of any type may lead to poor responsiveness, and should be avoided.

• Delaying computation until after the constructor may be an effective optimization; it may turn out to be unnecessary to perform all the work. This depends on the application, and shouldn't be determined prematurely.

• Overall, it depends.