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:
(name, Str#, "John")
or
(date, Date#, 2011-09-02)
(# is the Fantom way for specifying type: Str# is the 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.
--
Денис В. Шеломовский
Denis V. Shelomovskij
