[SOLVED] add custom operator support of extern class in C++ api

[steve3d]

I don't know if there is someone need this, but any script library should support custom operator export with c++.

 

Situation is I'm creating a date class to engine with boost::date_time, it's very convenient for any date plus some day or minus some day to get a new date with simple +/- operator. But uniginescript don't support operator export. So I have to write like

date d = new date("2012-2-29");
d.add(1);

 

although this can do most work, but if I want to add some day to a date and get a new date without change the original date class, this can not be done:

date d1 = new date("2012-2-29");
// want d2 to be 2012-3-1 while d1 still be 2012-2-29
date d2 = d1 +1;

 

any script library like lua/python all support of custom operator. So I need unigine also support this.

[steve3d]

and I don't think this is a very complex work, like Variable class already support in script class's operator. so adding this to extern class won't be a huge work.

[frustum]

What about the following solution:

class date {
 date() { datee = new date_extern(); }
 ~date() { delete datee; }
 date operator+(date d0,date d1) {
date ret = new date();
ret.datee.add(d0.datee,d1.datee);
return ret;
 }
 date_extern datee;
};

[steve3d]

I've thought about this when I post this thread, but this will require more action to be done, any project need date operation will need the date plugin and a script class, but before custom operator available to c++, this is the only way to make it work.

 

EDIT:

already tried with this, I need to write a wrapper class for whole c++ exported date class again in uniginescript...

 

I still have to say, support user class operator while not support c++ operator to script engine is not a so "powerful" script engine.

Edited July 9, 2012 by steve3d

[steve3d]

after some test and deep thought about this approach, this won't work at all. one big problem is user class don't support overloaded constructor.. and there is no assign operator( = operator).

 

so big problem if you create the class like this

class date {
 date(string ds) {
//...
 }
}

 

then you can only use a string to create a new date, and these code will be wrong

date d0 = new date("2012-2-20");
// create a not-a-date is not possible without overloaded constructor
// below line won't work
// date d1 = new date(); 
date d1 = d0;
d1 = d1 + 1;
// after this, right, d1 is 2012-2-21, but d1 is a reference to d0, so d0 also becomes 2012-2-21

 

this will cause a big problem!

[frustum]

Implementation of custom c++ operators is a simple task. But in this case you should respond to memory management and It will be not easy task.

For example if you have an operator+ for two objects which returns a new object. Who should delete this object? Or this object should be deleted automatically via reference counting system?

[steve3d]

like the boost::python did, it support both handling way of new object delete, the way of deleting the newly created object is specified with the export template function in c++.

 

Just leave it to user to decide this, you can set the new object to be deleted via reference counting system or by user himself.

 

EDIT:

 

need more about this, operator overload, adding two date is really impossible (it's useless to add 2012-2-20 with 2012-3-20, right? ), but in my case a date will need add weeks, months, years. so operator+ should support overload. ( this really useful to add 2 weeks, 3 months, years or more simple days to a date)

 

this should also applies to operator- . subtraction two date is meaningful.

[frustum]

It is not a rational idea since you will have to create multiple additional classes like Minute, Hour, Day, etc. to implement this feature in the object-oriented style.

Date date = new Date("2012");
date += new Minute(1);
date += new Hour(1);

In this case you operator+ should recognise different types of arguments (in pseudo syntax):

Date *operator+(Date *date,const Variable &v) {
 if(v.isMinute()) date += v.getMinute();
 if(v.isHour()) date += v.getHour();
}

I think this is a much harder than create several functions like addMinute/addHour into the Date class.

[steve3d]

I think we are talking about custom operator export, not how to create complete date calendar system, as to the hour mins things, they are not exist in boost::date_time for time calculation, there is time_duration class which has microsecond and nanosecond support. Adding months and weeks can be easily convert to adding days, date calculation don't need to care about hours , if you need hours and seconds , then use boost::posix_time. Please check www.boost.org for the details.

 

But I really need the custom operator even without the overloaded operator.

[frustum]

You can achieve absolutely the same result via:

• User class wrapper for C++ extern class
  
• Functions instead of operators
  

We'll consider your request, but there's far too many features to be implemented from a feature list, sorry.

[steve3d]

OK, after a deeper thought, I think there is no need to support a overloaded operator support in C++, just use Unigine::Variable as the operator argument, then this will solve the overloaded operator thing, in operator, user need to respond of distinguish the different type.

 

I think this is more simpler thing.

 

Well if you guys decided to not support this, I'll write a simpler date class by script.

[manguste]

A simpler approach is always good :)

[steve3d]

still need this, I've just created a script version of date class, but it still need a overloaded subtract operator, because there is no variable class in script, that Unigine::Variable only exists in c++ part, so a date can be subtracted by a int (days) or another date to get the days in between.

 

but with script class, it can not use variable as argument, so write code like

date d0 = new date("2012-2-23");
date d2 = new date("2011-2-23");

date d3 = d0 - 2; // to get 2012-2-21
int days = d0.daysBetween(d2);
/* that can not use
int days = d0 - d2;
*/

 

all this mathematical or logical operation must be used as a named function like add(), sub(), greater()... really looks ridiculous.

 

and to frustum, I saw in script, all operator returned a new variable class are all managed by the script's garbage collector, then why in c++ part, these new object should be user's respond to manage it's delete? it should be all managed by the garbage collector.

[frustum]

Bar is a wrapper for Foo class. You can simplify you mathematical operations if you want:

 

class Foo {
int a;
Foo() { }
Foo(int a_) { a = a_; }
Foo add(Foo f) { return new Foo(a + f.a); }
};

Foo f0 = new Foo(12);
Foo f1 = new Foo(13);
Foo f2 = f0.add(f1);
printf("%d\n",f2.a);

class Bar {
Foo foo;
Bar(int a) {
	if(is_int(a)) foo = new Foo(a);
	else foo = a;
}
Bar operator+(Bar b0,Bar b1) { return new Bar(b0.foo.add(b1.foo)); }
};

Bar b0 = new Bar(12);
Bar b1 = new Bar(13);
Bar b2 = b0 + b1;
printf("%d\n",b2.foo.a);

[steve3d]

Thanks again. And I'm already created a simple date class without any c++ plugin, the only problem is that I can not use date a - date b and date a-int days together.

 

But that's not a big problem, because dates subtraction is only usefull to interpolate two dates, so I created an interpolate function directly do this.

 

But I still hope unigine can support custom overloaded operator in c++ export

[manguste]

Sorry, not planned for the near future. Since there's an efficient workaround, we better focus on other issues from a wish list.