bool changes within Loki::StaticDispatcher

**Jan-Nik** · 08-05-2006

Hello!

I'm new to this forum and i'm not english. Hope you can help me either.

I can't understand, why the bool changes, although i'm not setting him to false anywhere:

Code:

#include <iostream>
#include <loki/MultiMethods.h>

struct Base
{
    virtual ~Base() {}
};

struct Widget : public Base
{
    Widget(int x = 0) : x_(x) {}
    int x_;
};

class HatchingExecutor
{
public:
    void Fire(Widget& lhs, Widget& rhs)
    {
        if(lhs.x_ == rhs.x_)
        {
            bool_ = true;
        }
        std::cout << "Bool: " << bool_ << " Adresse: " << &bool_ << std::endl;
    }
    void OnError(Base&, Base&) {}
    HatchingExecutor() : bool_(false) { std::cout << "Konstruktor" << std::endl; }
private:
    bool bool_;
};

int main()
{
    HatchingExecutor exec;
    typedef Loki::StaticDispatcher<HatchingExecutor, Base, LOKI_TYPELIST_1(Widget)> Dispatch;

    Widget a;
    Widget b(1);
    Widget c;

    Dispatch::Go(a, c, exec);
    Dispatch::Go(a, b, exec);
    Dispatch::Go(c, b, exec);
}

It shows:

Code:

Konstruktor
Bool: 1 Adresse: 0xbfae3368
Bool: 0 Adresse: 0xbfae3368
Bool: 0 Adresse: 0xbfae3368

I've suggested it would be one everytime, but where is it changed to false?

**SlyMaelstrom** · 08-05-2006

I've never heard of this Loki library and I'm sure it's not just me. If you're going to use non-standard libraries, it's best to post some code from that library, as well. Like, for instance, the Go() function and any function used in it.

**dwks** · 08-05-2006

If you're passing a copy of your class rather than a reference or a pointer, it would cause a new instance of it to be constructed. The if

Code:

        if(lhs.x_ == rhs.x_)
        {
            bool_ = true;
        }

might prove false, and bool_ would get the default boolean value, which is false. [edit] Or rather it would retain the value it was assigned in the constructor, as indicated two posts down. [/edit]

You could detect this by putting an else after the if:

Code:

else cout << "bool_ is now false\n";

You could fix this by removing the if or passing references/pointers.

[edit]

I've never heard of this Loki library

Where are your googling skills?

http://sourceforge.net/projects/loki-lib/ [/edit]

**SlyMaelstrom** · 08-05-2006

Originally Posted by dwks

[edit]

Where are your googling skills?

http://sourceforge.net/projects/loki-lib/ [/edit]

I'm not going to go hunting down code for some random person who chooses not to provide enough of it. I'm sure he would be willing to post the missing functions. However, if what I need to see to help isn't either in my knowledge bank or right in front of my eyes, I'm not going to put to much effort into an answer.

That's just me, though. It was kind of you to go searching for him.

**Mario F.** · 08-05-2006

The bool is being set to false on the class constructor.

Code:

HatchingExecutor() : bool_(false) { std::cout << "Konstruktor" << std::endl; }

**CornedBee** · 08-05-2006

Code behaves as by design. I don't know why you'd think it would be 1 every time.

For what it's worth, Loki is a library written by Andrei Alexandrescu as a general toolset and a companion for his book Modern C++ Design, which I highly recommend reading.

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