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In object oriented languages, it is fairly common to implement ASTs (Abstract Syntax Trees) using simple hierarchies (the Composite pattern), and to traverse them via visitors.
In functional programming languages, using variants/sum types, and then pattern matching, is the right approach.
C++ features both inheritance, and Boost.Variants. I have written several AST hierarchies using inheritance, but I'd like to get some feedback from people who would have used the variant approach. I'd like to know which one is the "best", in terms of performance (time and space), but also in terms of maintainability (easiness to create trees, and to traverse them).
I am especially interested in experience with implementation of hash-consing (keeping a single copy of each common subtree), possibly with Boost.Flyweight.
I am interested in battle field experience, not opinions. This question was original closed as "opinion-based". Which has never been the point...
Thanks!
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In this discussion, a poster (mikera) says
There's no dotted pair in Clojure.
A philosophical reason for this is that Clojure avoids the use of a
concrete "pair" data structure and instead emphasises abstract
"sequences" which can have may possible concrete implementations.
Can someone elaborate or point me to some literature on what this means? Is this a more elegant or mathematically pure approach?
Here is a link to a handy list of questions that Rich has answered about his design decisions https://gist.github.com/reborg/dc8b0c96c397a56668905e2767fd697f
While this list doesn't explicitly explain why there is no concrete "pair" data structure it might give you some insight into Rich's preference for practical, general design.
I remember there was a time when there was a discussion about introducing a "tuple" which would have been like a vector that only has two elements to avoid the needless memory allocation that occurs when using a two element vector.
Introducing these things has a complexity cost and so you can assume that the cost/benefit analysis did not warrant adding it to the code base.
Check out this discussion on Clojure's Jira project about adding tuples and you'll see how any idea gets put through its paces:
https://dev.clojure.org/jira/browse/CLJ-1517
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I've learned about data structures and algorithms in my university course and they taught us how to implement them. After reading some answers on SO and Quora, it seems that using the STL containers are recommended.
As a software engineer/developer, you should know how a particular data structure works under the hood. and you should be able to customize/invent one when you need it. that's the reason they thought you so.
But generally you won't need to reinvent the wheel. so when there are tried and tested data structures available, like the std::stack, there's no need to do it again. specially because you'll have more bug issues in your implementation than those of STL or any other well designed one like Boost.
Unless you think you have a better knowledge of software engineering than the designers of the STL - or you have some very specific hardware requirements that they are unaware of
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Let's suppose I'm writing a compiler for some programming language. It is common to use abstract syntax tree (AST) as an internal representation. I can see two possible ways to design it:
using boost::variant
using inheritance
As hierarchy of nodes is fixed - boost::variant will suffice.
My question is what are the advantages and disadvantages of each approach from points of maintability and runtime efficiency?
Using boost::variants will work, but will require you to use visitor pattern extensively to exploit the content of a variant object. If later you extend the number of types used in your variant, you'll have to maintain all the visitors that you've implemented.
With inheritance, you have the advantage of being able to use polymorphism. Later extension will be straightforward : simply derive one of the existing base and override the polymorphic functions, without touching the rest of the code.
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(Okay, so my previous question is on hold as being too broad, so I'm narrowing it down here.)
I'm looking to take part in algorithmic programming contests, and a lot of problems hinge on the use of specialized data structures which are extremely good at a certain operation - for example, Fenwick trees allow calculation of prefix sums of a list of values in logarithmic time.
What is the preferred way of implementing such data structures in modern C++ (i.e. using C++11 features)? Is it possible to use STL algorithms and containers instead of writing structs and coding every operation by hand?
I'm looking for Fenwick trees, segment trees, treaps and some other data structures often useful in IOI-style contests, but general strategies are more than enough.
there's an implementation of a fenwick tree here: http://www.algorithmist.com/index.php/Fenwick_tree
It uses std::vector as the underlying container.
arguably the method increase could be written in terms of std::transform or std::foreach.
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I've heard systems described as a "clean object model", but a precise definition does not seem to be around. It seems to refer to the classes being complete or consistent in some way.
I'm just wondering if it's referring to a specific trait or just another favorable term like 'elegant'.
Quantlib is described as "written in C++ with a clean object model".1
It's not really a technical term. A "clean" object model is a well-designed one, by whichever standard of good design. Usually it involved orthogonal classes with a clear separation of concerns and an intuitive mapping to real-world concepts, i.e. a lot of fuzziness that you'll need to judge for yourself.