• Dan (48/48) Mar 21 2013 I have an enum, say:
• =?UTF-8?B?QWxpIMOHZWhyZWxp?= (58/61) Mar 21 2013 It looks like fromJson must be a static member function because the

"Dan" <dbdavidson yahoo.com> writes:

I have an enum, say:

enum AssetCategory {
   Investment,
   PrimaryResidence,
   FamilyProperty,
   FinancialInstrument
}

and I have functions that convert to/from strings to be used in 
Json (via vibe json). The vibe wants to call out to user supplied 
toJson/fromJson if both functions are provided and the test for 
it is:

Json serializeToJson(T)(T value) {
...
  static if( __traits(compiles, value = 
T.fromJson(value.toJson())) ){
    return value.toJson();
...
}

I would like to use this feature to have the json output the 
string instead of numeric value (while still retaining numeric 
value in data structures). The toJson/fromJson functions below 
are close. They allow for this:

if( __traits(compiles, t.fromJson(t.toJson()) ))

to be true - but that is not the same thing. Is there a trickery 
to associate a static function with an enum? (e.g. 
AssetCategory.fromJson(json)) )

Thanks
Dan
-----------

static void fromJson(ref AssetCategory assetType, Json src) {
   string value = cast(string)src;
   writeln("value is ",value);
   final switch(value) {
   case "Investment": { assetType = AssetCategory.Investment; 
break; }
   case "PrimaryResidence": { assetType = 
AssetCategory.PrimaryResidence; break; }
   case "FamilyProperty": { assetType = 
AssetCategory.FamilyProperty; break; }
   case "FinancialInstrument": { assetType = 
AssetCategory.FinancialInstrument; break; }
   }
}

static Json toJson(AssetCategory assetType) {
   auto result = Json();
   result = text(assetType);
   return result;
}

=?UTF-8?B?QWxpIMOHZWhyZWxp?= <acehreli yahoo.com> writes:

On 03/21/2013 01:34 PM, Dan wrote:

 Json serializeToJson(T)(T value) {
 ...
 static if( __traits(compiles, value = T.fromJson(value.toJson())) ){

It looks like fromJson must be a static member function because the 
condition is written in a way that fromJson is called on the type 
itself. (I don't know any trick to bind that to a regular function.)

It may not be suitable in your case but wrapping the enum inside a 
struct is a solution (struct AssetCategory below):

import std.stdio;
import std.conv;

struct Json
{
     string s;

     this(string s) {
         writefln("constructing with %s", s);
         this.s = s;
     }

     T opCast(T : string)() const
     {
         return s;
     }
}

Json serializeToJson(T)(T value) {
     static if( __traits(compiles, value = T.fromJson(value.toJson())) )
     {
         return value.toJson();

     } else {
         return Json("NOT GOOD: DEFAULT BEHAVIOR");
     }
}

enum AssetCategoryType {
   Investment,
   PrimaryResidence,
   FamilyProperty,
   FinancialInstrument
}

struct AssetCategory
{
     AssetCategoryType assetType;

     alias assetType this;

     static AssetCategory fromJson(Json src) {
         string value = cast(string)src;
         return AssetCategory(value.to!AssetCategoryType);
     }
}

static Json toJson(AssetCategory assetType) {
   auto result = Json();
   result = Json(text(assetType));
   return result;
}

void main()
{
     auto category = AssetCategory(AssetCategoryType.FamilyProperty);
     auto json = serializeToJson(category);
     writeln(json);

     // Test fromJson
     assert(AssetCategory.fromJson(Json("PrimaryResidence")) ==
            AssetCategory(AssetCategoryType.PrimaryResidence));
}

Ali