digitalmars.D.learn - A "general" tag

Xan (20/20) Apr 14 2012 Hi,

"Aleksandar =?UTF-8?B?UnXFvmnEjWnEhyI=?= <aleksandar ruzicic.info> (6/27) Apr 14 2012 For "Type" look at enum (http://dlang.org/enum.html) and for

Xan (8/47) Apr 14 2012 I think it's not what I expect. Can I have a generic object type?

Denis Shelomovskij (68/112) Apr 16 2012 What you are looking for is a boxing.

Xan (4/134) Apr 16 2012 Uf!, it's more than I can process....

Marco Leise (19/21) Apr 25 2012 Too much information, yes. Too complicated no. :)

"Xan" <xancorreu gmail.com> writes:

Hi,

I try to translate a script I wrote in Fantom [www.fantom.org]. 
In my script, I have a type "Tag" defined as a triple of:
- String (the name of the tag),
- Type (the type of the tag: could be Str, Date, Int, etc.)
- Obj (the value of the tag; Fantom has Objects of Top-Class 
hierachy).

(normally the tag has Type = Obj.Type, but you can manually set).

For example,
you could have:


or





type)


Is there any way for emulating this? My main trouble is how to 
define Type and Object in D.

Thanks in advance,
Xan.

PS: Please, be patient, I'm a newbee.

Apr 14 2012

"Aleksandar =?UTF-8?B?UnXFvmnEjWnEhyI=?= <aleksandar ruzicic.info> writes:

On Saturday, 14 April 2012 at 19:17:52 UTC, Xan wrote:
 Hi,

 I try to translate a script I wrote in Fantom [www.fantom.org]. 
 In my script, I have a type "Tag" defined as a triple of:
 - String (the name of the tag),
 - Type (the type of the tag: could be Str, Date, Int, etc.)
 - Obj (the value of the tag; Fantom has Objects of Top-Class 
 hierachy).

 (normally the tag has Type = Obj.Type, but you can manually 
 set).

 For example,
 you could have:


 or





 type)


 Is there any way for emulating this? My main trouble is how to 
 define Type and Object in D.

 Thanks in advance,
 Xan.

 PS: Please, be patient, I'm a newbee.


For "Type" look at enum (http://dlang.org/enum.html) and for 
"Object" look at std.variant 
(http://dlang.org/phobos/std_variant.html).

And since Variant can tell you what type it contains you might no 
longer need that "Type" parameter.

Apr 14 2012

"Xan" <xancorreu gmail.com> writes:

On Saturday, 14 April 2012 at 19:40:06 UTC, Aleksandar Ružičić 
wrote:
 On Saturday, 14 April 2012 at 19:17:52 UTC, Xan wrote:
 Hi,

 I try to translate a script I wrote in Fantom 
 [www.fantom.org]. In my script, I have a type "Tag" defined as 
 a triple of:
 - String (the name of the tag),
 - Type (the type of the tag: could be Str, Date, Int, etc.)
 - Obj (the value of the tag; Fantom has Objects of Top-Class 
 hierachy).

 (normally the tag has Type = Obj.Type, but you can manually 
 set).

 For example,
 you could have:


 or





 type)


 Is there any way for emulating this? My main trouble is how to 
 define Type and Object in D.

 Thanks in advance,
 Xan.

 PS: Please, be patient, I'm a newbee.


 For "Type" look at enum (http://dlang.org/enum.html) and for 
 "Object" look at std.variant 
 (http://dlang.org/phobos/std_variant.html).

 And since Variant can tell you what type it contains you might 
 no longer need that "Type" parameter.

I think it's not what I expect. Can I have a generic object type? 
Something like an assigment like:

Any a


?

With templates?

Please, guide me. I'm a newbee

Apr 14 2012

Denis Shelomovskij <verylonglogin.reg gmail.com> writes:

15.04.2012 0:31, Xan написал:
 On Saturday, 14 April 2012 at 19:40:06 UTC, Aleksandar Ružičić wrote:
 On Saturday, 14 April 2012 at 19:17:52 UTC, Xan wrote:
 Hi,

 I try to translate a script I wrote in Fantom [www.fantom.org]. In my
 script, I have a type "Tag" defined as a triple of:
 - String (the name of the tag),
 - Type (the type of the tag: could be Str, Date, Int, etc.)
 - Obj (the value of the tag; Fantom has Objects of Top-Class hierachy).

 (normally the tag has Type = Obj.Type, but you can manually set).

 For example,
 you could have:


 or







 Is there any way for emulating this? My main trouble is how to define
 Type and Object in D.

 Thanks in advance,
 Xan.

 PS: Please, be patient, I'm a newbee.


 For "Type" look at enum (http://dlang.org/enum.html) and for "Object"
 look at std.variant (http://dlang.org/phobos/std_variant.html).

 And since Variant can tell you what type it contains you might no
 longer need that "Type" parameter.

 I think it's not what I expect. Can I have a generic object type?
 Something like an assigment like:

 Any a


 ?

 With templates?

 Please, guide me. I'm a newbee

What you are looking for is a boxing.
http://en.wikipedia.org/wiki/Boxing_(computer_science)#Boxing

D doesn't support auto boxing/unboxing. For a reason see, e.g. this thread:
http://forum.dlang.org/thread/ckoaum$1lbg$1 digitaldaemon.com
http://forum.dlang.org/thread/cr7njl$18j3$1 digitaldaemon.com

There was std.boxer module, but it was deprecated and removed, this is 
the last version before removal:
https://github.com/D-Programming-Language/phobos/blob/c20d454d63861a0c4bab647b37c01b0dd981a3f8/std/boxer.d

std.variant is really what you are looking for. See example:
---
import std.stdio;
import std.variant;
import std.string: format;

struct Tag {
     string name;
     Variant entity;
}

class C {
     int i;

     this(int i) { this.i = i; }

     string toString() { return format("C(i: %s)", i); }
}

struct SmallStruct {
     int a;
}

struct Huge {
     real a, b, c, d, e, f, g;
}

void writeTag(Tag tag) {
     writeln(tag);
     with(tag.entity)
         if(auto intVal = peek!int()) {
             writeln("  Contains int: ", *intVal);
             // Arithmetic is supported too
             writeln("  + 3: ", tag.entity + 3);
             writeln("  * 2: ", tag.entity * 2);
         } else if(auto hugeVal = peek!Huge())
             // Don't use *hugeVal for now, there is a bug in peek
             writeln("  Contains Huge struct: ", tag.entity.get!Huge());
         else if(auto classInfo = cast(TypeInfo_Class)type)
             writefln("  Contains class %s: %s", classInfo.name, 
get!Object());
         else if(auto structInfo = cast(TypeInfo_Struct)type)
             writefln("  Contains struct %s: %s", structInfo.name, 
tag.entity);
         // else if etc.
}

void main() {
     writeTag(Tag("tag1", Variant(12)));
     writeTag(Tag("tag2", Variant("str")));
     writeTag(Tag("tag3", Variant(["str1", "str2"])));
     writeTag(Tag("tag4", Variant(new C(17))));
     writeTag(Tag("tag4", Variant(SmallStruct(3))));
     // Variant isn't enough to hold Huge so a copy
     // will be accocated in GC heap.
     // Yes, this isn't documented yet and `peek` will give you garbage
     // for this case because of a bug.
     writeTag(Tag("tag4", Variant(Huge(1.1, 2.2, 3.3, 4.4, 5.5, 6.6, 
7.7))));
}
---

std.variant has some bugs for now but is usable:
http://d.puremagic.com/issues/buglist.cgi?query_format=advanced&short_desc=variant&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&short_desc_type=allwords

Templates are usable in other cases, not this.

-- 
Денис В. Шеломовский
Denis V. Shelomovskij

Apr 16 2012

"Xan" <xancorreu gmail.com> writes:

Uf!, it's more than I can process....
It's really a **complicated** thing to do that in D.

On Monday, 16 April 2012 at 07:50:28 UTC, Denis Shelomovskij
wrote:
 15.04.2012 0:31, Xan написал:
 On Saturday, 14 April 2012 at 19:40:06 UTC, Aleksandar 
 Ružičić wrote:
 On Saturday, 14 April 2012 at 19:17:52 UTC, Xan wrote:
 Hi,

 I try to translate a script I wrote in Fantom 
 [www.fantom.org]. In my
 script, I have a type "Tag" defined as a triple of:
 - String (the name of the tag),
 - Type (the type of the tag: could be Str, Date, Int, etc.)
 - Obj (the value of the tag; Fantom has Objects of Top-Class 
 hierachy).

 (normally the tag has Type = Obj.Type, but you can manually 
 set).

 For example,
 you could have:


 or





 sys::Str type)


 Is there any way for emulating this? My main trouble is how 
 to define
 Type and Object in D.

 Thanks in advance,
 Xan.

 PS: Please, be patient, I'm a newbee.


 For "Type" look at enum (http://dlang.org/enum.html) and for 
 "Object"
 look at std.variant 
 (http://dlang.org/phobos/std_variant.html).

 And since Variant can tell you what type it contains you 
 might no
 longer need that "Type" parameter.

 I think it's not what I expect. Can I have a generic object 
 type?
 Something like an assigment like:

 Any a


 ?

 With templates?

 Please, guide me. I'm a newbee

 What you are looking for is a boxing.
 http://en.wikipedia.org/wiki/Boxing_(computer_science)#Boxing

 D doesn't support auto boxing/unboxing. For a reason see, e.g. 
 this thread:
 http://forum.dlang.org/thread/ckoaum$1lbg$1 digitaldaemon.com
 http://forum.dlang.org/thread/cr7njl$18j3$1 digitaldaemon.com

 There was std.boxer module, but it was deprecated and removed, 
 this is the last version before removal:
 https://github.com/D-Programming-Language/phobos/blob/c20d454d63861a0c4bab647b37c01b0dd981a3f8/std/boxer.d

 std.variant is really what you are looking for. See example:
 ---
 import std.stdio;
 import std.variant;
 import std.string: format;

 struct Tag {
     string name;
     Variant entity;
 }

 class C {
     int i;

     this(int i) { this.i = i; }

     string toString() { return format("C(i: %s)", i); }
 }

 struct SmallStruct {
     int a;
 }

 struct Huge {
     real a, b, c, d, e, f, g;
 }

 void writeTag(Tag tag) {
     writeln(tag);
     with(tag.entity)
         if(auto intVal = peek!int()) {
             writeln("  Contains int: ", *intVal);
             // Arithmetic is supported too
             writeln("  + 3: ", tag.entity + 3);
             writeln("  * 2: ", tag.entity * 2);
         } else if(auto hugeVal = peek!Huge())
             // Don't use *hugeVal for now, there is a bug in 
 peek
             writeln("  Contains Huge struct: ", 
 tag.entity.get!Huge());
         else if(auto classInfo = cast(TypeInfo_Class)type)
             writefln("  Contains class %s: %s", classInfo.name, 
 get!Object());
         else if(auto structInfo = cast(TypeInfo_Struct)type)
             writefln("  Contains struct %s: %s", 
 structInfo.name, tag.entity);
         // else if etc.
 }

 void main() {
     writeTag(Tag("tag1", Variant(12)));
     writeTag(Tag("tag2", Variant("str")));
     writeTag(Tag("tag3", Variant(["str1", "str2"])));
     writeTag(Tag("tag4", Variant(new C(17))));
     writeTag(Tag("tag4", Variant(SmallStruct(3))));
     // Variant isn't enough to hold Huge so a copy
     // will be accocated in GC heap.
     // Yes, this isn't documented yet and `peek` will give you 
 garbage
     // for this case because of a bug.
     writeTag(Tag("tag4", Variant(Huge(1.1, 2.2, 3.3, 4.4, 5.5, 
 6.6, 7.7))));
 }
 ---

 std.variant has some bugs for now but is usable:
 http://d.puremagic.com/issues/buglist.cgi?query_format=advanced&short_desc=variant&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&short_desc_type=allwords

 Templates are usable in other cases, not this.

Apr 16 2012

Marco Leise <Marco.Leise gmx.de> writes:

Am Mon, 16 Apr 2012 20:52:16 +0200
schrieb "Xan" <xancorreu gmail.com>:

 Uf!, it's more than I can process....
 It's really a **complicated** thing to do that in D.

Too much information, yes. Too complicated no. :)
D is statically typed (Fantom allows both static and dynamic typing). That
means that for every variable in your program you know beforehand what type it
is. You say you have String, Type and Obj. Here we cannot say what type Obj is,
because it depends on what Type says. Now you want something from a statically
typed language, that it wasn't designed for.

You may want to adapt to the style of a statically typed language and use a
struct:

import std.datetime;

struct Person {
	string name;  // a person has a field 'name' of type string
	Date   date;
}

This means that you cannot change the type of 'date' or 'name', and you cannot
have a person without a date.

If you really, *really*, REALLY need the full flexibility, you can use
Variants. You can store any data in a Variant, so it would replace Type and Obj
in your code.

struct Tag {
	string description; // <String>: store "name", "date", etc. in this
	Variant data;       // <Type & Obj>: store "John" or Date(2012, 4, 25) in this
}

Many more solutions are possible, but we'd need to take a look at your code.
Also one solution may be more flexible while another is faster. It depends a
bit on what you expect. Every language has its pros and cons. Dynamic typing is
not one of D's strengths, but execution speed is, for example.

-- 
Marco

Apr 25 2012

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digitalmars.D.learn - A "general" tag