Add compile time switch to alter encoder enum representation

json_serialization/format.nim

@@ -20,12 +20,31 @@ template supports*(_: type Json, T: type): bool =
   # The JSON format should support every type
   true
 
+type
+  EnumRepresentation* = enum
+    EnumAsString
+    EnumAsNumber
+    EnumAsStringifiedNumber
+
 template flavorUsesAutomaticObjectSerialization*(T: type DefaultFlavor): bool = true
 template flavorOmitsOptionalFields*(T: type DefaultFlavor): bool = true
 template flavorRequiresAllFields*(T: type DefaultFlavor): bool = false
 template flavorAllowsUnknownFields*(T: type DefaultFlavor): bool = false
 template flavorSkipNullFields*(T: type DefaultFlavor): bool = false
 
+var DefaultFlavorEnumRep {.compileTime.} = EnumAsString
+template flavorEnumRep*(T: type DefaultFlavor): EnumRepresentation =
+  DefaultFlavorEnumRep
+
+template flavorEnumRep*(T: type DefaultFlavor, rep: static[EnumRepresentation]) =
+  static:
+    DefaultFlavorEnumRep = rep
+
+# If user choose to use `Json` instead of `DefaultFlavor`, it still goes to `DefaultFlavor`
+template flavorEnumRep*(T: type Json, rep: static[EnumRepresentation]) =
+  static:
+    DefaultFlavorEnumRep = rep
+
 # We create overloads of these traits to force the mixin treatment of the symbols
 type DummyFlavor* = object
 template flavorUsesAutomaticObjectSerialization*(T: type DummyFlavor): bool = true
@@ -53,3 +72,11 @@ template createJsonFlavor*(FlavorName: untyped,
   template flavorRequiresAllFields*(T: type FlavorName): bool = requireAllFields
   template flavorAllowsUnknownFields*(T: type FlavorName): bool = allowUnknownFields
   template flavorSkipNullFields*(T: type FlavorName): bool = skipNullFields
+
+  var `FlavorName EnumRep` {.compileTime.} = EnumAsString
+  template flavorEnumRep*(T: type FlavorName): EnumRepresentation =
+    `FlavorName EnumRep`
+
+  template flavorEnumRep*(T: type FlavorName, rep: static[EnumRepresentation]) =
+    static:
+      `FlavorName EnumRep` = rep

json_serialization/writer.nim

@@ -271,6 +271,21 @@ proc writeJsonValueRef*[F,T](w: var JsonWriter[F], value: JsonValueRef[T]) =
   of JsonValueKind.Null:
     append "null"
 
+template writeValue*(w: var JsonWriter, value: enum) =
+  # We extract this as a template because
+  # if we put it into `proc writeValue` below
+  # the Nim compiler generic cache mechanism
+  # will mess up with the compile time
+  # conditional selection
+  mixin writeValue
+  type Flavor = type(w).Flavor      
+  when Flavor.flavorEnumRep() == EnumAsString:
+    w.writeValue $value
+  elif Flavor.flavorEnumRep() == EnumAsNumber:
+    w.stream.writeText(value.int)
+  elif Flavor.flavorEnumRep() == EnumAsStringifiedNumber:
+    w.writeValue $value.int
+
 proc writeValue*(w: var JsonWriter, value: auto) {.gcsafe, raises: [IOError].} =
   mixin writeValue
 
@@ -332,10 +347,7 @@ proc writeValue*(w: var JsonWriter, value: auto) {.gcsafe, raises: [IOError].} =
 
   elif value is bool:
     append if value: "true" else: "false"
-
-  elif value is enum:
-    w.writeValue $value
-
+
   elif value is range:
     when low(typeof(value)) < 0:
       w.stream.writeText int64(value)

tests/test_json_flavor.nim

@@ -132,3 +132,71 @@ suite "Test JsonFlavor":
     # field should not processed at all
     let y = NullyFields.decode(jsonTextWithNullFields, ListOnly)
     check y.list.string.len == 0
+
+  test "Enum value representation primitives":
+    when NullyFields.flavorEnumRep() == EnumAsString:
+      check true
+    elif NullyFields.flavorEnumRep() == EnumAsNumber:
+      check false
+    elif NullyFields.flavorEnumRep() == EnumAsStringifiedNumber:
+      check false
+
+    NullyFields.flavorEnumRep(EnumAsNumber)
+    when NullyFields.flavorEnumRep() == EnumAsString:
+      check false
+    elif NullyFields.flavorEnumRep() == EnumAsNumber:
+      check true
+    elif NullyFields.flavorEnumRep() == EnumAsStringifiedNumber:
+      check false
+
+    NullyFields.flavorEnumRep(EnumAsStringifiedNumber)
+    when NullyFields.flavorEnumRep() == EnumAsString:
+      check false
+    elif NullyFields.flavorEnumRep() == EnumAsNumber:
+      check false
+    elif NullyFields.flavorEnumRep() == EnumAsStringifiedNumber:
+      check true
+
+  test "Enum value representation of custom flavor":
+    type
+      ExoticFruits = enum
+        DragonFruit
+        SnakeFruit
+        StarFruit
+
+    NullyFields.flavorEnumRep(EnumAsNumber)
+    let u = NullyFields.encode(DragonFruit)
+    check u == "0"
+
+    NullyFields.flavorEnumRep(EnumAsString)
+    let v = NullyFields.encode(SnakeFruit)
+    check v == "\"SnakeFruit\""
+
+    NullyFields.flavorEnumRep(EnumAsStringifiedNumber)
+    let w = NullyFields.encode(StarFruit)
+    check w == "\"2\""
+
+  test "EnumAsString of custom flavor":
+    type
+      Fruit = enum
+        Banana = "BaNaNa"
+        Apple  = "ApplE"
+        JackFruit = "VVV"
+
+    NullyFields.flavorEnumRep(EnumAsString)
+    let u = NullyFields.encode(Banana)
+    check u == "\"BaNaNa\""
+
+    let v = NullyFields.encode(Apple)
+    check v == "\"ApplE\""
+
+    let w = NullyFields.encode(JackFruit)
+    check w == "\"VVV\""
+
+    NullyFields.flavorEnumRep(EnumAsStringifiedNumber)
+    let x = NullyFields.encode(JackFruit)
+    check x == "\"2\""
+
+    NullyFields.flavorEnumRep(EnumAsNumber)
+    let z = NullyFields.encode(Banana)
+    check z == "0"

tests/test_writer.nim

@@ -168,3 +168,71 @@ suite "Test writer":
     check uu.string == """{"a":123,"b":"nano","c":456}"""
     let vv = YourJson.encode(y)
     check vv.string == """{"a":null,"b":null,"c":999}"""
+
+  test "Enum value representation primitives":
+    when DefaultFlavor.flavorEnumRep() == EnumAsString:
+      check true
+    elif DefaultFlavor.flavorEnumRep() == EnumAsNumber:
+      check false
+    elif DefaultFlavor.flavorEnumRep() == EnumAsStringifiedNumber:
+      check false
+
+    DefaultFlavor.flavorEnumRep(EnumAsNumber)
+    when DefaultFlavor.flavorEnumRep() == EnumAsString:
+      check false
+    elif DefaultFlavor.flavorEnumRep() == EnumAsNumber:
+      check true
+    elif DefaultFlavor.flavorEnumRep() == EnumAsStringifiedNumber:
+      check false
+
+    DefaultFlavor.flavorEnumRep(EnumAsStringifiedNumber)
+    when DefaultFlavor.flavorEnumRep() == EnumAsString:
+      check false
+    elif DefaultFlavor.flavorEnumRep() == EnumAsNumber:
+      check false
+    elif DefaultFlavor.flavorEnumRep() == EnumAsStringifiedNumber:
+      check true
+
+  test "Enum value representation of DefaultFlavor":
+    type
+      ExoticFruits = enum
+        DragonFruit
+        SnakeFruit
+        StarFruit
+
+    DefaultFlavor.flavorEnumRep(EnumAsNumber)
+    let u = Json.encode(DragonFruit)
+    check u == "0"
+
+    DefaultFlavor.flavorEnumRep(EnumAsString)
+    let v = Json.encode(SnakeFruit)
+    check v == "\"SnakeFruit\""
+
+    DefaultFlavor.flavorEnumRep(EnumAsStringifiedNumber)
+    let w = Json.encode(StarFruit)
+    check w == "\"2\""
+
+  test "EnumAsString of DefaultFlavor/Json":
+    type
+      Fruit = enum
+        Banana = "BaNaNa"
+        Apple  = "ApplE"
+        JackFruit = "VVV"
+
+    Json.flavorEnumRep(EnumAsString)
+    let u = Json.encode(Banana)
+    check u == "\"BaNaNa\""
+
+    let v = Json.encode(Apple)
+    check v == "\"ApplE\""
+
+    let w = Json.encode(JAckFruit)
+    check w == "\"VVV\""
+
+    Json.flavorEnumRep(EnumAsStringifiedNumber)
+    let x = Json.encode(JackFruit)
+    check x == "\"2\""
+
+    Json.flavorEnumRep(EnumAsNumber)
+    let z = Json.encode(Banana)
+    check z == "0"