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Six222

Global & Static Classes

5 posts in this topic

Hey guys, I'm current working on my next game and I've made a couple so far but I've always felt that the code that I wrote for them is messy. I'm forever making every class global or static just so I can access them from somewhere else instead of having to pass refrences around. For example:

[code]
class EntityHandler
{
public:
void Tick();
void Draw();

static void AddNewEntity();
static void AddBullet();
private:
static vector<Bullet>BulletList;
static vector<Enemy>EnemyList;
};
[/code]
I'm writing all of my classes like this just so I can add a new entity/bullet from anywhere in my code. Looking at I feel that it's correct, it works but I can't help thinking that it's just a bad way of programming.

I could just send a refrence to the EntityHandler to every class but the entities shouldn't have to know about that and I would also probably be sending in loads of other refrences to all the static classes I have just so I could perform 1 or 2 tasks. This isn't good but I honestly don't know how I could do it another way. I guess some sort of message/event system could work for this but I really don't know...

Anyway If anyone could point me in the right direction that would be awesome. Thanks
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You are right in that it is not the best solution. You are also right in that giving each class reference to EntityHandler would be a bad idea as it requires boilerplate code and creates minor memory overhead.

A slightly better approach (although not the best imho) would be something like this:
[code]
class EntityHandler {
public:
void Tick();
void Draw();

void AddNewEntity();
void AddBullet();

private:
vector<bullet> BulletList;
vector<enemy> EnemyList;
};


class Global {
private:
static EntityHandler entityHandler;

public:
static EntityHandler& getEntityHandler();
};
[/code]

This way at least EntityHandler is no longer static and its instances can be used elsewhere when required.

However, accessing Global::getEntityHandler() is a bit unwieldy and the rest of the code will become dependent on global instances.
The solution I usually prefer is to instead have a non-static class and pass its reference on only to methods that actually need it:
[code]
class EntityHandler {
public:
void Tick();
void Draw();

void AddNewEntity();
void AddBullet();

private:
vector<bullet> BulletList;
vector<enemy> EnemyList;
};

class Bullet {
public:
// Pass the reference of EntityHandler only to methods that actually require it
// or some other class containing EntityHandler reference.
// This way you won't have to worry about EntityHandler being destroyed before bullet as it would be generally
// passed from EntityHandler::Tick/Draw method.
// It would also be completely painless to take a Bullet from one EntityHandler and put it to another as there
// is no internal reference.
void Tick(EntityHandler& e);
void Draw(EntityHandler& e);
};
[/code]

It might seem to be a bit of a hassle to pass it on to such functions, but there are generally quite few functions that should need to see something as grand as EntityHandler.
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I never thought of passing the EntityHandler down through like that /facepalm.. So I could for example do this?

[code]
class Bullet {
public:
void Tick(EntityHandler& e);
void Draw(EntityHandler& e);
};

void EntityHandler::Tick()
{
vector<bullet>::Iterator it;
for(it = BulletList.begin(); it != BulletList.end(); it++)
{
(*it)->Tick(*this);
}
}

[/code]
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[quote name='mrjones' timestamp='1330529809' post='4917786']
Precisely. I didn't write that part down before, but that is exactly what I meant.
[/quote]

I started re-writing some of the static classes to pass the EntityHandler down and other classes and it works well. Thanks for the help!
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Also don't forget about namespaces, I never used to use them and now use them everywhere, they are really handy for wrapping things up and making it all a bit neater.
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