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Showing posts from 2018

Inheritance vs std::variant

C++17 added std::variant and std::visit in its repertoire. They are worth a close examination. I've been wondering about whether they are always better than inheritance for modeling sum-types (fancy name for discriminated unions) and if not, under what circumstances they are not. We'll compare the two approaches in this blog post. So here it goes.

Inheritancestd::variantNeed not know all the derived types upfront (open-world assumption)Must know all the cases upfront (closed-world assumption)Dynamic Allocation (usually)No dynamic allocationIntrusive (must inherit from the base class)Non-intrusive (third-party classes can participate)Reference semantics (think how you copy a vector of pointers to base class?)Value semantics (copying is trivial)Algorithm scattered into classesAlgorithm in one placeLanguage supported (Clear errors if pure-virtual is not implemented)Library supported (poor error messages)Creates a first-class abstractionIt’s just a containerKeeps fluent interfaces…