www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - compile time introspection and code generation - automatically serialize to json

reply Tobias Pankrath <tobias pankrath.net> writes:
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
Jul 21 2011
next sibling parent Robert Clipsham <robert octarineparrot.com> writes:
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/
Jul 21 2011
prev sibling next sibling parent Robert Clipsham <robert octarineparrot.com> writes:
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/
Jul 21 2011
prev sibling next sibling parent reply Jacob Carlborg <doob me.com> writes:
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
Jul 21 2011
parent reply Tobias Pankrath <tobias pankrath.net> writes:
 
 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
Jul 21 2011
parent Jacob Carlborg <doob me.com> writes:
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
Jul 21 2011
prev sibling parent Adam Ruppe <destructionator gmail.com> writes:
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
}
Jul 21 2011