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    <p>The rationale for not doing any work in the constructor comes from looking at the execution of the program in two phases. The first phase is to wire up your object graph. The second phase is to do the "real work".</p> <p>There is a tension between this ideal and efficiently maintaining a class's invariants and internal state. The less setup you can do in your constructor, the more difficult all of your methods will be to implement because they must take into account the varying possible internal state of the object. Remember, the constructor is the only code you can be sure is called for an object.</p> <p>The way out of this conundrum is to realize that an object's "real work" is defined by it's interface and behavior in relation to other objects. That is, the dependencies provided to the constructor and objects provided as arguments to methods later down the road. </p> <p>Feel free to do any kind of setup you like in your constructor that does not have a noticeable effect on other objects in your system. Likewise, be very sensitive to timing issues in your object's construction.</p> <p>If you determine that a File object can't exist without a filename provided by the user: don't call keyboard.filename_from_keyboard() in the constructor. Instead you design your system such that the object is created by a factory (provider) during execution with the filename provided to the constructor or you allow the File object to exist without a filename. Maybe it can get it's own filename during execution? This is part of managing your object's lifetime and it's the hardest part IMO. This gets very subtle because "real work" involves creating objects too. But I digress...</p> <p>In your example you would have to decide if foo.GetBuzz() breaks that condition. If GetBuzz() is a referentially transparent function, you're almost always in the clear to call it in the constructor. If GetBuzz() involves any I/O, user interaction or changes any noticeable internal state of any other object, then it is probably does not need to be called from a constructor.</p>
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    1. POIs non-trivial constructor in IoC paradigm a bad thing?
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    1. CONice considerations. However, how I can know (in general case), that some method call in **interface** will involve I/O , or network call? It is abstracted away!
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    2. COObviously you want to err on the side of NOT calling the method in the constructor. Generally speaking, don't do it ever. This a weak form of coupling that you have to evaluate on a case by case basis.
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    3. COYou asked about including non-trivial logic. If you know that a method call is non-trivial or trivial on another object, then you've already pierced the abstraction boundary with your knowledge of the inner workings of the other object. If that really bothers you (and it should at least a little bit), assume every operation is non-trivial and do nothing in the constructor. This is the most pessimistic view you can take.
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