Hi,

I have a class which has already an alias this to a string array,
so I can use it in a foreach loop.

class MyClass
{
	string[] _data;
	alias _data this;
	// ...
}

void main()
{
	import std.json;
	auto jsValue = JSONValue(new MyClass());
}

For some generic code I need an implicit conversion of MyClass so I can
use it for a JSONValue. For the coding above I receive a compiler error:
static assert  "unable to convert type "MyClass" to json"

Is there anything I can do?

Kind regards
André

On Thursday, 24 March 2016 at 08:15:12 UTC, Andre wrote:
> Hi,
>
> I have a class which has already an alias this to a string array,
> so I can use it in a foreach loop.
>
> class MyClass
> {
> 	string[] _data;
> 	alias _data this;
> 	// ...
> }
>
> void main()
> {
> 	import std.json;
> 	auto jsValue = JSONValue(new MyClass());
> }
>
> For some generic code I need an implicit conversion of MyClass so I can
> use it for a JSONValue. For the coding above I receive a compiler error:
> static assert  "unable to convert type "MyClass" to json"


JSONValue only works with the build in types, not with user defined types. Either you define a specific function for the class that returns a JSONValue. Easiest way to do that would be to build an associative array with strings as keys with the names, and JSONValues as values and turn that into JSONValue, i.e. (untested):
class MyClass
{
	string[] _data;
	alias _data this;
	// ...
   JSONValue toJSON()
  {
    JSONValue[string] aa;
    JSONValue[] dataJSON = _data.map!((a) => JSONValue(a)).array;
    aa["data"] = JSONValue(dataJSON);
    return JSONValue(aa);
  }
}

Alternatively there are multiple serialization libraries that will allow you to turn any user defined type from and to JSONValues.

https://code.dlang.org/packages/painlessjson
https://code.dlang.org/packages/jsonizer

Cheers, Edwin

On Thursday, 24 March 2016 at 08:24:46 UTC, Edwin van Leeuwen wrote:
> Alternatively there are multiple serialization libraries that will allow you to turn any user defined type from and to JSONValues.
>
> https://code.dlang.org/packages/painlessjson
> https://code.dlang.org/packages/jsonizer
>
> Cheers, Edwin

I don't know the above libraries so I can't comment on their quality, but I've used vibe.d's json module extensively and it's pretty solid. Vibe has also recently been split up into multiple subpackages, so you only have to depend on vibe-d:data and don't have to pull in the rest.

On Thursday, 24 March 2016 at 08:24:46 UTC, Edwin van Leeuwen wrote:
> JSONValue only works with the build in types, not with user defined types. Either you define a specific function for the class that returns a JSONValue. Easiest way to do that would be to build an associative array with strings as keys with the names, and JSONValues as values and turn that into JSONValue, i.e. (untested):
> class MyClass
> {
> 	string[] _data;
> 	alias _data this;
> 	// ...
>    JSONValue toJSON()
>   {
>     JSONValue[string] aa;
>     JSONValue[] dataJSON = _data.map!((a) => JSONValue(a)).array;
>     aa["data"] = JSONValue(dataJSON);
>     return JSONValue(aa);
>   }
> }
>

isnt alias this supposed to do this implicitly?

convert this
auto jsValue = JSONValue(new MyClass());

into this
auto jsValue = JSONValue((new MyClass())._data);

On Thursday, 24 March 2016 at 11:39:13 UTC, arturg wrote:
> isnt alias this supposed to do this implicitly?
>
> convert this
> auto jsValue = JSONValue(new MyClass());
>
> into this
> auto jsValue = JSONValue((new MyClass())._data);

Good point, I did not catch that. That indeed should work and seems to be a bug. Does it work if _data is a base type (string or int, etc..)

On Thursday, 24 March 2016 at 16:03:13 UTC, Edwin van Leeuwen wrote:
> On Thursday, 24 March 2016 at 11:39:13 UTC, arturg wrote:
>> isnt alias this supposed to do this implicitly?
>>
>> convert this
>> auto jsValue = JSONValue(new MyClass());
>>
>> into this
>> auto jsValue = JSONValue((new MyClass())._data);
>
> Good point, I did not catch that. That indeed should work and seems to be a bug. Does it work if _data is a base type (string or int, etc..)

Thanks for the answers. I also wonder why alias this does not the job.
Unfortunatelly even if it works, the _data is not the data I want to be used
as value for JSONValue. _data only contains keys, the values are stored
in another variable. JSONValue should contain both.

I hoped there is some operator overloading for implicit conversion of my
class to JSONValue.
I solved the issue with an toJSON method and a generic functionality which
checks for this method.

Kind regards
André

On Thursday, 24 March 2016 at 17:03:25 UTC, Andre wrote:
> I hoped there is some operator overloading for implicit conversion of my
> class to JSONValue.
> I solved the issue with an toJSON method and a generic functionality which
> checks for this method.
>
> Kind regards
> André


Vibe.d has some serialization with toJson(), fromJson() methods:
http://vibed.org/api/vibe.data.json/serializeToJson
Maybe you can work with that?