Comments on: Writing functional code in C++ IV – Algebraic datatypes http://lucabolognese.wordpress.com/2012/04/27/writing-functional-code-in-c-iv-algebraic-datatypes/ x += x++; Fri, 03 May 2013 18:26:20 +0000 hourly 1 http://wordpress.com/ By: lucabol http://lucabolognese.wordpress.com/2012/04/27/writing-functional-code-in-c-iv-algebraic-datatypes/#comment-229 Mon, 23 Jul 2012 17:25:46 +0000 https://lucabolognese.wordpress.com/?p=92#comment-229 Hi Clement,
Yes, you can simulate algebraic datatypes with inheritance and type testing, albeit more verbosely and less efficiently. The if(true) thing is just a bug. Probably at some point in the coding the condition was a bit more interesting.

]]> By: Clément http://lucabolognese.wordpress.com/2012/04/27/writing-functional-code-in-c-iv-algebraic-datatypes/#comment-228 Sat, 21 Jul 2012 11:30:47 +0000 https://lucabolognese.wordpress.com/?p=92#comment-228 I’ve developped this idea on my own blog, http://pit-claudel.fr/clement/blog/using-abstract-classes-to-simulate-tagged-unions-aka-sum-types/

]]> By: Clément http://lucabolognese.wordpress.com/2012/04/27/writing-functional-code-in-c-iv-algebraic-datatypes/#comment-227 Sat, 21 Jul 2012 11:27:20 +0000 https://lucabolognese.wordpress.com/?p=92#comment-227 Amusing solution! I’d like to expend on the first few lines of your article though:
“Very roughly, where object orientation uses derivation, functional programming uses algebraic datatypes. ”

Expanding on this, you could implement your LivinEntity type like this:

#include

using namespace std;

class LivingEntity {
public:
string name;
virtual void print() = 0;

LivingEntity(string name) {
this->name = name;
}

class Person;
class Dog;
};

class LivingEntity::Person : LivingEntity {
public:
Person(string name) : LivingEntity(name) {}

void print() {
cout << "I am a per named " << name << endl;
}
};

class LivingEntity::Dog : LivingEntity {
public:
Dog(string name) : LivingEntity(name) {}

void print() {
cout << "I am a dog named " << name << endl;
}
};

int main()
{
LivingEntity::Dog a_dog = LivingEntity::Dog("a dog");
LivingEntity::Person a_person = LivingEntity::Person("a person");
a_dog.print();
a_person.print();
return 0;
}

Also, why do you use else if(true) { __VA_ARGS__} instead of just else { __VA_ARGS__} in your macros?

Thanks for the nice article!

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