[GiNaC-list] list of list

[Jerome BENOIT]

Hello,

thanks for the reply.

Actually I use list of lists to perform quick test.

A last question:
is there any king of NULL (as in Maple) object in GiNaC ?

Thanks in advance,
Jerome

Sheplyakov Alexei wrote:
> Hello,
> 
> On Sun, Feb 04, 2007 at 02:19:42AM +0800, Jerome BENOIT wrote:
>> I have just noticed that:
>>
>> lst list;
>> list = lst(lst(1,1),lst(2,4),lst(3,9));
>>
>> gives a list of list as expected,
>> whereas
>>
>> lst list;
>> list = lst(1,1),lst(2,4),lst(3,9);
> 
> Probably you want this:
> 
> list = ex(lst(1, 1)), lst(2, 4), lst(3,9);
>  
>> gives the first list (namely lst(1,1))
> 
> Not exactly, your code gives lst(1, 1) as opposed to lst(lst(1, 1)).
> 
>> is it a bug ?
> 
> No. This is how C++ function overload resolution works. There are several
> overloaded instances of operator= in the lst class:
> 
> lst& operator=(const lst&);
> container_init<ex, std::list> operator=(const ex&);
> 
> First one gives the best match (no type conversion form lst
> to ex is necessary), so your code basically reads as:
> 
> class foo {
> 	int i;
> 	public:
> 	foo();
> 	foo(int i_);
> 	foo& operator=(const foo& o);
> };
> 
> void demo() {
> 	// lst list;
> 	foo a; 
> 	// list = lst(1, 1), lst(2, 4), lst(3, 9);
> 	a = foo(1), foo(2), foo(3);
> }
> 
> foo::foo() { i = 0; }
> foo::foo(int i_) { i = i_; }
> foo& foo::operator=(const foo& o) {
> 	if (&o != this)
> 		i = o.i;
> 	return *this;
> }
> 
>> or is it a wrong thing to do ? 
> 
> There is nothing wrong about list of lists. But the code operating on
> such lists will be [probably] somewhat inefficient.
> 
> Best regards,
>  Alexei
> 

-- 
Jerome BENOIT
jgmbenoit_at_mailsnare_dot_net