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/*

# Pure virtual from constructor

Calling virtual method from base constructor is not possible

http://stackoverflow.com/questions/496440/c-virtual-function-from-constructor

Not possible because derived class has not yet been initialized.

Workaround? http://www.parashift.com/c%2B%2B-faq-lite/calling-virtuals-from-ctor-idiom.html

*/

#include "common.hpp"

int main() {

// Basic example.

{

class Base {

public:

int i;

int j;

Base() {

this->i = a();

// LINKER ERROR: undefined reference to b().

//this->j = b();

}

virtual int a() { return 0; }

virtual int b() = 0;

int c() { return b(); }

};

class Derived : public Base {

public:

virtual int a() { return 1; }

virtual int b() { return 2; }

};

Derived c;

// Base::a is called not Derived::a

// because it is the constructor.

assert(c.i == 0);

// Base::b is called because we are not in the constructor.

assert(c.c() == 2);

}

// The simplest solution seems to be to define a separate init function.

// Downside: requires you to write a new constructor on the derived, and forward all arguments.

{

class Base {

public:

int i;

int j;

Base() {}

void init() {

this->i = a();

this->j = b();

}

virtual int a() { return 0; }

virtual int b() = 0;

};

class Derived : public Base {

public:

Derived() { init(); }

virtual int a() { return 1; }

virtual int b() { return 2; }

};

Derived c;

assert(c.i == 1);

assert(c.j == 2);

}

}