Why this code can't take advantage from CTFE?

[Luis via Digitalmars-d-learn]

On Friday, 5 February 2016 at 09:36:37 UTC, Andrea Fontana wrote:
> On Wednesday, 3 February 2016 at 22:45:47 UTC, Timon Gehr wrote:
>> I would use enum forceCTFE(alias expr)=expr; though. With 
>> alias it won't force compile-time evaluation of expressions 
>> that can be interpreted as symbols.
>
> I've a code that build a JSON object using a wrapper over 
> std.json.
>
> This code:
>
> ----
>
> enum forceCTFE(alias expr)=expr;
>
> auto j = forceCTFE!(
>   JSOB
>   (
>     "hello", JSOB("world", 3),
>     "arr", JSAB("hello", JSOB("world", 1))
>   )
> );
>
> j.put("/hello/world", "!");
> j.put("/hello/blah", 42);	
> // Here j == 
> {"arr":["hello",{"world":1}],"hello":{"blah":42,"world":"!"}}


Reading/parsing a JSON or a XML using std.json / std.xml could be 
done on CTFE ?