eventpp/doc/eventmaker.md

# Event maker macros reference

## Overview

`eventpp/utilities/eventmaker.h` contains several macros to generate event classes.  
Without the macros, we may need to repeat the same code structure on lots of event classes.  
For example,  

```c++
// The base event
class Event
{
};

class EventMouseDown : public Event
{
public:
    int getX() const;
    int getY() const;
    int getButton() const;
    
private:
    int x;
    int y;
    int button;
};

class EventKeyDown : public Event
{
public:
    int getKey() const;
    
private:
    int key;
};

```

It's not rare that there are dozens of or even hundreds of event classes in a system, and we need to repeat the same code structure many times, which is boring and error prone.  

The macros in eventmaker.h can reduce the work significantly.

## Header

eventpp/utilities/eventmaker.h

## Macro EVENTPP_MAKE_EVENT
```c++
#define EVENTPP_MAKE_EVENT(className, baseClassName, baseClassArgs, ...)
```

EVENTPP_MAKE_EVENT declares an event class.  

**className**: the event class name.  
**baseClassName**: the class name that the event inherits from. The macro requires a base class. If the class name contains comma (,), such as a template class, it should be enclosed within parenthesis. Examples, `Event`, `(AnotherEvent<int, char>)`.  
**baseClassArgs**: the arguments passed to the base class. If the arguments contain comma (,), it should be enclosed within parenthesis. If there is no arguments for the base class, `()` can be used.  
**The variadic arguments (...)**: the tuples of member data type and getter/setter function name. A tuple is elements in a pair of parenthesis. A tuple can contain 2 or 3 elements, the first element is the data type, the second element is the getter function name, and the optional third element is the setter function name. Some tuples examples: `(int, getX)`, `(std::string, getText, setText)`.  
Note: the variadic arguments can't be empty. If the even class doesn't have data member, use `EVENTPP_MAKE_EMPTY_EVENT` instead.

The macro always generates a default constructor and a constructor that takes all data members and initialize them.  

Code examples:  
```c++
EVENTPP_MAKE_EVENT(
    EventDraw, Event, EventType::draw,
    (std::string, getText, setText), (int, getX), (double, getSize)
);
```
Generates class like (in pseudo code),
```c++
class EventDraw : public Event
{
public:
    EventDraw(const std::string & text, const int x, const double size)
        : Event(EventType::draw), text(text), x(x), size(size)
    {
    }
    
    const std::string & getText() const {
        return text;
    }
    
    void setText(const std::string & value) {
        text = value;
    }
    
    const int getX() const {
        return x;
    }
    
    const double getSize() const {
        return size;
    }

private:
    std::string text;
    int x;
    double size;
};

```

```c++
EVENTPP_MAKE_EVENT(EventDraw, (Event<int, char>), EventType::draw,
    (std::string, getText, setText), (int, getX), (double, getSize)
);
```
Similar to above example, except the base class is `Event<int, char>`.  

```c++
EVENTPP_MAKE_EVENT(EventDraw, (Event<int, char>), (EventType::draw, 5),
    (std::string, getText, setText), (int, getX), (double, getSize)
);
```
Similar to above example, except the base class is constructed with `(EventType::draw, 5)` instead of `(EventType::draw)`.  


## Macro EVENTPP_MAKE_EMPTY_EVENT
```c++
#define EVENTPP_MAKE_EMPTY_EVENT(className, baseClassName, baseClassArgs)
```

Similar with `EVENTPP_MAKE_EVENT`, but EVENTPP_MAKE_EMPTY_EVENT declares event class which doesn't have any data member.

## Tip: add getter/setter prefix automatically

If you don't want to specify "get" or "set" prefix explictly, or you want the field definition looks like a property rather than getter/setter function, you can define some auxiliary macros to achieve that. For example,

```
// auto add "get" prefix
#define G(type, name) (type, get ## name)

// auto add "get" and "set" prefix
#define GS(type, name) (type, get ## name, set ## name)

EVENTPP_MAKE_EVENT(EventDrawGS, Event, EventType::draw,
	GS(std::string, Text),
	G(int, X),
	G(double, Size)
);
```

Of course you need to choose better macro names than `G` and `GS`, or `#undef` them after using them.