Hi everyone,

I'm taking a look at D again and asked myself, if
it is possible to write a template mixin or something
similiar that automatically serializes an object to json.

For example:

class MyClass
{
    string memberA;
    int memberB;
    MyClass memberC;
    mixin ToJson!MyClass;
}

should make possible to automatically output
"someid" { "memberA" : "somestring",
	"memberB" : 12,
	memberC : "someotherid"};

How could this be accomplished? I've found std.traits
RepresentationTypeTupel but don't see how this would
help me.

Thanks,

Tobias

On 21/07/2011 08:57, Tobias Pankrath wrote:
> Hi everyone,
>
> I'm taking a look at D again and asked myself, if
> it is possible to write a template mixin or something
> similiar that automatically serializes an object to json.
>
> For example:
>
> class MyClass
> {
>      string memberA;
>      int memberB;
>      MyClass memberC;
>      mixin ToJson!MyClass;
> }
>
> should make possible to automatically output
> "someid" { "memberA" : "somestring",
> 	"memberB" : 12,
> 	memberC : "someotherid"};
>
> How could this be accomplished? I've found std.traits
> RepresentationTypeTupel but don't see how this would
> help me.
>
> Thanks,
>
> Tobias
>
>

Something like this is very possible, here's a start for you (untested, sorry about the awkward indentation):

----
mixin template ToJson(T)
{
  string toJson()
  {
    foreach (i, member; T.tupleof)
    {
        enum memberName = T.tupleof[i].stringof[
				T.stringof.length + 3 .. $
				];
        writefln("%s : %s", memberName, member);
    }
    assert(0, "Eventually this should return a json string, "
              "but for now it just asserts");
  }
}
someInstanceOfMyClass.toJson();
----

I'll leave it at this and leave you to figure out the rest - just ask if you get stuck :)

-- 
Robert
http://octarineparrot.com/

On 21/07/2011 08:57, Tobias Pankrath wrote:
> Hi everyone,
>
> I'm taking a look at D again and asked myself, if
> it is possible to write a template mixin or something
> similiar that automatically serializes an object to json.
>
> For example:
>
> class MyClass
> {
>      string memberA;
>      int memberB;
>      MyClass memberC;
>      mixin ToJson!MyClass;
> }
>
> should make possible to automatically output
> "someid" { "memberA" : "somestring",
> 	"memberB" : 12,
> 	memberC : "someotherid"};
>
> How could this be accomplished? I've found std.traits
> RepresentationTypeTupel but don't see how this would
> help me.
>
> Thanks,
>
> Tobias
>
>

Side note: If/when you finish this, you should definitely make a pull request for phobos' std.json! This sort of thing would be incredibly useful!

-- 
Robert
http://octarineparrot.com/

On 2011-07-21 09:57, Tobias Pankrath wrote:
> Hi everyone,
>
> I'm taking a look at D again and asked myself, if
> it is possible to write a template mixin or something
> similiar that automatically serializes an object to json.
>
> For example:
>
> class MyClass
> {
>      string memberA;
>      int memberB;
>      MyClass memberC;
>      mixin ToJson!MyClass;
> }
>
> should make possible to automatically output
> "someid" { "memberA" : "somestring",
> 	"memberB" : 12,
> 	memberC : "someotherid"};
>
> How could this be accomplished? I've found std.traits
> RepresentationTypeTupel but don't see how this would
> help me.
>
> Thanks,
>
> Tobias

Have a look at Orange: http://www.dsource.org/projects/orange
I'm in a middle of a complete rewrite but you can use a previous version (if it still works) or look at the code.

-- 
/Jacob Carlborg

> 
> Have a look at Orange: http://www.dsource.org/projects/orange
> I'm in a middle of a complete rewrite but you can use a previous version
> (if it still works) or look at the code.
> 
Thank you for pointing me there. Looks very interesting. I took a quick look at the code and got some questions. I found this pattern quite often in phobos sources, too.

Why do you declare in Reflection.d[1] a template parameterNamesOf(alias func) and one called parameterNamesOfImpl? Wouldn't be one sufficient?

I do understand the case if you want to use the template recursively and
hide one parameter like in fieldsOf / fieldsOfImpl.
Though I don't understand why you are using a recursive template in fieldsOf
and a imperative function in parameterNamesOfImpl? Is it possible to you use
both in both places?



[1] http://www.dsource.org/projects/orange/browser/orange/util/Reflection.d

For another implementation, find the functions toJson and toJsonValue in my web.d

http://arsdnet.net/dcode/web.d


Bascially: foreach(member; item.tupleof) {
   static if(is(typeof(member) == something)
     json it
   else static if.... repeat for supported type families
}

On 2011-07-21 13:09, Tobias Pankrath wrote:
>>
>> Have a look at Orange: http://www.dsource.org/projects/orange
>> I'm in a middle of a complete rewrite but you can use a previous version
>> (if it still works) or look at the code.
>>
> Thank you for pointing me there. Looks very interesting. I took a quick look
> at the code and got some questions. I found this pattern quite often in
> phobos sources, too.
>
> Why do you declare in Reflection.d[1] a template
> parameterNamesOf(alias func) and one called parameterNamesOfImpl? Wouldn't
> be one sufficient?
>
> I do understand the case if you want to use the template recursively and
> hide one parameter like in fieldsOf / fieldsOfImpl.
> Though I don't understand why you are using a recursive template in fieldsOf
> and a imperative function in parameterNamesOfImpl? Is it possible to you use
> both in both places?
>
>
>
> [1] http://www.dsource.org/projects/orange/browser/orange/util/Reflection.d

The thought behind that was that I wanted to force the function to be used at compile time. But now when I think about it you could just declare the argument as a template argument on the regular function.

-- 
/Jacob Carlborg