design - Where does idea that "inheritance is to be avoided" originate from? -

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recently discussed defect mentioned here , 1 of parties said "yes, that's why books inheritance should avoided.

i've been using inheritance years , find useful , convenient in many design cases. i'm sure person arguing @ least misunderstood "books say".

is there idea inheritance kind of bad , should avoided? originate , can learn more?

i think might have meant inheritance can overused, in cases composition better solution. discussed in several books, e.g.

inheritance powerful way achieve code reuse, not best tool job. used inappropriately, leads fragile software. safe use inheritance within package, subclass , superclass implementations under control of same programmers. safe use inheritance when extending classes designed , documented extension (item 17). inheriting ordinary concrete classes across package boundaries, however, dangerous. reminder, book uses word “inheritance” mean implementation inheritance (when 1 class extends another). problems discussed in item not apply interface inheritance (when class implements interface or 1 interface extends another).

unlike method invocation, inheritance violates encapsulation [snyder86]. in other words, subclass depends on implementation details of superclass proper function. superclass’s implementation may change release release, , if does, subclass may break, though code has not been touched. consequence, subclass must evolve in tandem superclass, unless superclass’s authors have designed , documented purpose of being extended.

  • effective c++ 3rd edition has several items related this:
    • item 32: make sure public inheritance models "is-a."
    • item 34: differentiate between inheritance of interface , inheritance of implementation
    • item 38: model "has-a" or "is-implemented-in-terms-of" through composition

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