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Ashkan

Unity On Combining Compile-time and Run-time Polymorphism

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I've had lots of headaches in the past regarding this issue. It seems as if templates and generic programming on one hand and runtime polymorphism on the other, cause lots of frictions. To give you guys a taste of what I'm talking about, here is the latest issue I bumped into lately. The general idea is really simple. I was tired of GetFirstElement(), GetNextElement() functions in my interfaces so I decided to provide some STL-compliant iterators in an effort to eliminate those functions. After all, that's what iterators excel at, right? Now this is really simple if 1) You are willing to impose some restrictions on the TYPE of the container that implementors of this interface should use. OR 2) You are willing to make all such interfaces generic. This is nasty. None of these options is really appealing. So I simply decided to provide some sort of a base iterator class, so all implementors of the said interface can also provide some derived iterator types that best know how to traverse them. Pretty sweet, huh? All I wanted was STL-compliant iterators with runtime polymorphic behavior. Don't be fooled though! THAT WAS A PROGRAMMER'S WORST NIGHTMARE! Templates are like the plague. They just want to procreate and reproduce themselves all over the place. So I got down to thinking, coding, searching and reading for more than 12 freaking hours and just about every time I was on the verge of getting it solved, something would magically happen out of the blue as if it was not meant to be solved. It was an insane experience. I've come to believe over the course of the years that every problem in the field of programming has at least one relatively simple solution to it and if you can't find a moderate solution to the problem, chances are you won't find a solution at all! And just before I was about to totally give up the idea, I came by any_iterator by Thomas Becker and there I found an article On the Tension Between Object-Oriented and Generic Programming in C++. WOW! I was astonished that he had the exact same problem as me. So in an effort to share what I learned today here I am posting this. What do you think?

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