Usage of custom class with JSONValue

[Edwin van Leeuwen via Digitalmars-d-learn]

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