So what is the use of these boxes? I can not undestand? Can someone help me... maybe a little example and explanation why it is needed? Thank you...

Boxing is basically wannabe loose typing.  It's for use when you want to pass something around without the baton holders having to know the type of it.

It's like a void*, except with type information.  Or, so I understand.

-[Unknown]


> So what is the use of these boxes? I can not undestand? Can someone help me...
> maybe a little example and explanation why it is needed? Thank you...
> 
> 

> So what is the use of these boxes? I can not undestand? Can someone help
> me...
> maybe a little example and explanation why it is needed? Thank you...

Synonims:
   VARIANT,
   discriminated union.

Box is a structure which stores polymorphic data (not known at compile time)
Typically implemented as
struct box
{
   byte type; // type of data in the box
   union {
      int intVal;
      double dblVal;
      void* ptrVal;
   } data;

   int getIntData() {  if(type == INT) return data.intVal; .... }
   double getDblData() {  .... }
}

Almost all scripting languages use kind of boxes as a representation of values.

Andrew.





"bobef" <bobef_member@pathlink.com> wrote in message news:d6is5q$2gt9$1@digitaldaemon.com...
> So what is the use of these boxes? I can not undestand? Can someone help
> me...
> maybe a little example and explanation why it is needed? Thank you...
>
> 

"Andrew Fedoniouk" <news@terrainformatica.com> wrote in message news:d6jglj$2v9l$1@digitaldaemon.com...
>> So what is the use of these boxes? I can not undestand? Can someone help
>> me...
>> maybe a little example and explanation why it is needed? Thank you...
>
> Synonims:
>   VARIANT,
>   discriminated union.
>
> Box is a structure which stores polymorphic data (not known at compile
> time)
> Typically implemented as
> struct box
> {
>   byte type; // type of data in the box
>   union {
>      int intVal;
>      double dblVal;
>      void* ptrVal;
>   } data;
>
>   int getIntData() {  if(type == INT) return data.intVal; .... }
>   double getDblData() {  .... }
> }
>
> Almost all scripting languages use kind of boxes as a representation of values.
>
> Andrew.

I agree Box is like discriminated unions in that they store data whose type is only known at run time but I wouldn't say it's a synonym since as you pointed out in a previous thread unions wrap a small number of known types and Boxes wrap all types. Maybe I'm nit-picking...

> I agree Box is like discriminated unions in that they store data whose type is only known at run time but I wouldn't say it's a synonym since as you pointed out in a previous thread unions wrap a small number of known types and Boxes wrap all types. Maybe I'm nit-picking...

:) Well, well, well,  back to roots....
... let me to take my place on the rostrum... ok...
(who the hell left this chalk here?) .... khm-khm....

Dear students!
...
Discriminated union is such a type (especially an algebraic data type) might
be
described as a discriminated union if it is a sum type whose objects consist
of a
tag to say which part of the union they belong to and a value of the
corresponding type.
...
(Hooh, too long statement... not for use in MSDN...)

To be serious:
Andrew's Alexandrescu discriminated unions implementation
based on type lists is just a particular case of them.
The Box is another implementation of DU limited by
type system of D language.

:-P

Andrew.



"Ben Hinkle" <ben.hinkle@gmail.com> wrote in message news:d6jiik$306n$1@digitaldaemon.com...
>
> "Andrew Fedoniouk" <news@terrainformatica.com> wrote in message news:d6jglj$2v9l$1@digitaldaemon.com...
>>> So what is the use of these boxes? I can not undestand? Can someone help
>>> me...
>>> maybe a little example and explanation why it is needed? Thank you...
>>
>> Synonims:
>>   VARIANT,
>>   discriminated union.
>>
>> Box is a structure which stores polymorphic data (not known at compile
>> time)
>> Typically implemented as
>> struct box
>> {
>>   byte type; // type of data in the box
>>   union {
>>      int intVal;
>>      double dblVal;
>>      void* ptrVal;
>>   } data;
>>
>>   int getIntData() {  if(type == INT) return data.intVal; .... }
>>   double getDblData() {  .... }
>> }
>>
>> Almost all scripting languages use kind of boxes as a representation of values.
>>
>> Andrew.
>
> I agree Box is like discriminated unions in that they store data whose type is only known at run time but I wouldn't say it's a synonym since as you pointed out in a previous thread unions wrap a small number of known types and Boxes wrap all types. Maybe I'm nit-picking...
> 

So why don't we just use void*-s? Their content is also know at run time. I mean we know what we put in there so we know what we expect to put out. Or at least most of the cases. Anyway I think I understand it better now but I still can't think of any use.. I don't say it is useless I just can't think of one in this moment...


In article <d6jglj$2v9l$1@digitaldaemon.com>, Andrew Fedoniouk says...
>
>> So what is the use of these boxes? I can not undestand? Can someone help
>> me...
>> maybe a little example and explanation why it is needed? Thank you...
>
>Synonims:
>   VARIANT,
>   discriminated union.
>
>Box is a structure which stores polymorphic data (not known at compile time)
>Typically implemented as
>struct box
>{
>   byte type; // type of data in the box
>   union {
>      int intVal;
>      double dblVal;
>      void* ptrVal;
>   } data;
>
>   int getIntData() {  if(type == INT) return data.intVal; .... }
>   double getDblData() {  .... }
>}
>
>Almost all scripting languages use kind of boxes as a representation of values.
>
>Andrew.
>
>
>
>
>
>"bobef" <bobef_member@pathlink.com> wrote in message news:d6is5q$2gt9$1@digitaldaemon.com...
>> So what is the use of these boxes? I can not undestand? Can someone help
>> me...
>> maybe a little example and explanation why it is needed? Thank you...
>>
>> 
>
>

The idea is simply to have a class to put both a void* in and a TypeInfo, essentially.

The use might be for something like this:

Box coolfunction(int mode)
{
	if (mode == 1)
		return box(5);
	elseif (mode == 2)
		return box("testing");
	else
		return box(false);
}

Or similar.  For class members too.

-[Unknown]


> So why don't we just use void*-s? Their content is also know at run time. I mean
> we know what we put in there so we know what we expect to put out. Or at least
> most of the cases. Anyway I think I understand it better now but I still can't
> think of any use.. I don't say it is useless I just can't think of one in this
> moment...

Thanks. I understand now. It is cool. I like it.

In article <d6k5fl$fda$1@digitaldaemon.com>, Unknown W. Brackets says...
>
>The idea is simply to have a class to put both a void* in and a TypeInfo, essentially.
>
>The use might be for something like this:
>
>Box coolfunction(int mode)
>{
>	if (mode == 1)
>		return box(5);
>	elseif (mode == 2)
>		return box("testing");
>	else
>		return box(false);
>}
>
>Or similar.  For class members too.
>
>-[Unknown]
>
>
>> So why don't we just use void*-s? Their content is also know at run time. I mean we know what we put in there so we know what we expect to put out. Or at least most of the cases. Anyway I think I understand it better now but I still can't think of any use.. I don't say it is useless I just can't think of one in this moment...

"Unknown W. Brackets" <unknown@simplemachines.org> wrote in message news:d6k5fl$fda$1@digitaldaemon.com...
> The idea is simply to have a class to put both a void* in and a TypeInfo, essentially.

A small clarification: an important feature is that integer types like ints, longs and doubles and array-references (ptr + length) are stored "inline" meaning what is stored is not a void* pointing to an int but the actual int is stored. So it is very efficient to pass around boxes of small types like ints.

bobef wrote:
> So why don't we just use void*-s? Their content is also know at run time. I mean we know what we put in there so we know what we expect to put out. Or at least most of the cases. Anyway I think I understand it better now but I still can't think of any use.. I don't say it is useless I just can't think of one in this moment...
> 
> 
> In article <d6jglj$2v9l$1@digitaldaemon.com>, Andrew Fedoniouk says...
> 
>>>So what is the use of these boxes? I can not undestand? Can someone help
>>>me...
>>>maybe a little example and explanation why it is needed? Thank you...
>>
>>Synonims:
>>  VARIANT,
>>  discriminated union.
>>
>>Box is a structure which stores polymorphic data (not known at compile time)
>>Typically implemented as
>>struct box
>>{
>>  byte type; // type of data in the box
>>  union {
>>     int intVal;
>>     double dblVal;
>>     void* ptrVal;
>>  } data;
>>
>>  int getIntData() {  if(type == INT) return data.intVal; .... }
>>  double getDblData() {  .... }
>>}
>>
>>Almost all scripting languages use kind of boxes as a representation of values.
>>
>>Andrew.
>>
>>
>>
>>
>>
>>"bobef" <bobef_member@pathlink.com> wrote in message news:d6is5q$2gt9$1@digitaldaemon.com...
>>
>>>So what is the use of these boxes? I can not undestand? Can someone help
>>>me...
>>>maybe a little example and explanation why it is needed? Thank you...
>>>
>>>
>>
>>
> 
> 

Dang, I'm gone for a while, and a neat feature like this gets added... This'll be great for implementing a scripting language in my game engine.. :)

-- 
-PIB

--
"C++ also supports the notion of *friends*: cooperative classes that are permitted to see each other's private parts." - Grady Booch