[Go] Make enums into real types, add String() (#5235)

* [Go] Make enums into real types, add String()

This changes the generated code for enums: instead of type aliases,
they're now distinct types, allowing for better type-checking. Some
client code may have to be changed to add casts.

Enum types now have a String() method, so they implement fmt.Stringer.

An EnumValues map is now generated, in addition to the existing
EnumNames map, to easily map strings to values.

Generated enum files are now gofmt-clean.

Fixes #5207

* use example.ColorGreen explicitly

* use valid enum value in mutation test, add new test for "invalid" enum

* add length check and comment

src/idl_gen_go.cpp

@@ -83,7 +83,7 @@ class GoGenerator : public BaseGenerator {
       if (parser_.opts.one_file) {
         one_file_code += enumcode;
       } else {
-        if (!SaveType(**it, enumcode, false)) return false;
+        if (!SaveType(**it, enumcode, false, true)) return false;
       }
     }
 
@@ -95,13 +95,14 @@ class GoGenerator : public BaseGenerator {
       if (parser_.opts.one_file) {
         one_file_code += declcode;
       } else {
-        if (!SaveType(**it, declcode, true)) return false;
+        if (!SaveType(**it, declcode, true, false)) return false;
       }
     }
 
     if (parser_.opts.one_file) {
       std::string code = "";
-      BeginFile(LastNamespacePart(go_namespace_), true, &code);
+      const bool is_enum = !parser_.enums_.vec.empty();
+      BeginFile(LastNamespacePart(go_namespace_), true, is_enum, &code);
       code += one_file_code;
       const std::string filename = GeneratedFileName(path_, file_name_);
       return SaveFile(filename.c_str(), code, false);
@@ -140,7 +141,7 @@ class GoGenerator : public BaseGenerator {
     code += "\n}\n\n";
   }
 
-  // Construct the name of the type alias for this enum.
+  // Construct the name of the type for this enum.
   std::string GetEnumTypeName(const EnumDef &enum_def) {
     return WrapInNameSpaceAndTrack(cur_name_space_, GoIdentity(enum_def.name));
   }
@@ -148,8 +149,8 @@ class GoGenerator : public BaseGenerator {
   // Create a type for the enum values.
   void GenEnumType(const EnumDef &enum_def, std::string *code_ptr) {
     std::string &code = *code_ptr;
-    code += "type " + GetEnumTypeName(enum_def) + " = ";
-    code += GenTypeBasic(enum_def.underlying_type) + "\n";
+    code += "type " + GetEnumTypeName(enum_def) + " ";
+    code += GenTypeBasic(enum_def.underlying_type) + "\n\n";
   }
 
   // Begin enum code with a class declaration.
@@ -160,12 +161,13 @@ class GoGenerator : public BaseGenerator {
 
   // A single enum member.
   void EnumMember(const EnumDef &enum_def, const EnumVal &ev,
-                  std::string *code_ptr) {
+                  const int max_name_length, std::string *code_ptr) {
     std::string &code = *code_ptr;
     code += "\t";
     code += enum_def.name;
     code += ev.name;
     code += " ";
+    code += std::string(max_name_length - ev.name.length(), ' ');
     code += GetEnumTypeName(enum_def);
     code += " = ";
     code += enum_def.ToString(ev) + "\n";
@@ -177,7 +179,7 @@ class GoGenerator : public BaseGenerator {
     code += ")\n\n";
   }
 
-  // Begin enum name code.
+  // Begin enum name map.
   void BeginEnumNames(const EnumDef &enum_def, std::string *code_ptr) {
     std::string &code = *code_ptr;
     code += "var EnumNames";
@@ -187,22 +189,63 @@ class GoGenerator : public BaseGenerator {
 
   // A single enum name member.
   void EnumNameMember(const EnumDef &enum_def, const EnumVal ev,
-                      std::string *code_ptr) {
+                      const int max_name_length, std::string *code_ptr) {
     std::string &code = *code_ptr;
     code += "\t";
     code += enum_def.name;
     code += ev.name;
-    code += ":\"";
+    code += ": ";
+    code += std::string(max_name_length - ev.name.length(), ' ');
+    code += "\"";
     code += ev.name;
     code += "\",\n";
   }
 
-  // End enum name code.
+  // End enum name map.
   void EndEnumNames(std::string *code_ptr) {
     std::string &code = *code_ptr;
     code += "}\n\n";
   }
 
+  // Generate String() method on enum type.
+  void EnumStringer(const EnumDef &enum_def, std::string *code_ptr) {
+    std::string &code = *code_ptr;
+    code += "func (v " + enum_def.name + ") String() string {\n";
+    code += "\tif s, ok := EnumNames" + enum_def.name + "[v]; ok {\n";
+    code += "\t\treturn s\n";
+    code += "\t}\n";
+    code += "\treturn \""+ enum_def.name;
+    code += "(\" + strconv.FormatInt(int64(v), 10) + \")\"\n";
+    code += "}\n\n";
+  }
+
+  // Begin enum value map.
+  void BeginEnumValues(const EnumDef &enum_def, std::string *code_ptr) {
+    std::string &code = *code_ptr;
+    code += "var EnumValues";
+    code += enum_def.name;
+    code += " = map[string]" + GetEnumTypeName(enum_def) + "{\n";
+  }
+
+  // A single enum value member.
+  void EnumValueMember(const EnumDef &enum_def, const EnumVal ev,
+                       const int max_name_length, std::string *code_ptr) {
+    std::string &code = *code_ptr;
+    code += "\t\"";
+    code += ev.name;
+    code += "\": ";
+    code += std::string(max_name_length - ev.name.length(), ' ');
+    code += enum_def.name;
+    code += ev.name;
+    code += ",\n";
+  }
+
+  // End enum value map.
+  void EndEnumValues(std::string *code_ptr) {
+    std::string &code = *code_ptr;
+    code += "}\n\n";
+  }
+
   // Initialize a new struct or table from existing data.
   void NewRootTypeFromBuffer(const StructDef &struct_def,
                              std::string *code_ptr) {
@@ -281,9 +324,11 @@ class GoGenerator : public BaseGenerator {
     GenReceiver(struct_def, code_ptr);
     code += " " + MakeCamel(field.name);
     code += "() " + TypeName(field) + " {\n";
-    code += "\treturn " + getter;
-    code += "(rcv._tab.Pos + flatbuffers.UOffsetT(";
-    code += NumToString(field.value.offset) + "))\n}\n";
+    code += "\treturn " + CastToEnum(
+        field.value.type,
+        getter + "(rcv._tab.Pos + flatbuffers.UOffsetT(" +
+        NumToString(field.value.offset) + "))");
+    code += "\n}\n";
   }
 
   // Get the value of a table's scalar.
@@ -295,8 +340,9 @@ class GoGenerator : public BaseGenerator {
     GenReceiver(struct_def, code_ptr);
     code += " " + MakeCamel(field.name);
     code += "() " + TypeName(field) + " ";
-    code += OffsetPrefix(field) + "\t\treturn " + getter;
-    code += "(o + rcv._tab.Pos)\n\t}\n";
+    code += OffsetPrefix(field) + "\t\treturn ";
+    code += CastToEnum(field.value.type, getter + "(o + rcv._tab.Pos)");
+    code += "\n\t}\n";
     code += "\treturn " + GenConstant(field) + "\n";
     code += "}\n\n";
   }
@@ -364,7 +410,7 @@ class GoGenerator : public BaseGenerator {
     std::string &code = *code_ptr;
     GenReceiver(struct_def, code_ptr);
     code += " " + MakeCamel(field.name) + "(";
-    code += "obj " + TypeName(field) + ") bool ";
+    code += "obj " + GenTypePointer(field.value.type) + ") bool ";
     code += OffsetPrefix(field);
     code += "\t\t" + GenGetter(field.value.type);
     code += "(obj, o)\n\t\treturn true\n\t}\n";
@@ -395,8 +441,7 @@ class GoGenerator : public BaseGenerator {
     code += "}\n\n";
   }
 
-  // Get the value of a vector's non-struct member. Uses a named return
-  // argument to conveniently set the zero value for the result.
+  // Get the value of a vector's non-struct member.
   void GetMemberOfVectorOfNonStruct(const StructDef &struct_def,
                                     const FieldDef &field,
                                     std::string *code_ptr) {
@@ -408,10 +453,11 @@ class GoGenerator : public BaseGenerator {
     code += "(j int) " + TypeName(field) + " ";
     code += OffsetPrefix(field);
     code += "\t\ta := rcv._tab.Vector(o)\n";
-    code += "\t\treturn " + GenGetter(field.value.type) + "(";
-    code += "a + flatbuffers.UOffsetT(j*";
-    code += NumToString(InlineSize(vectortype)) + "))\n";
-    code += "\t}\n";
+    code += "\t\treturn " + CastToEnum(
+        field.value.type,
+        GenGetter(field.value.type) + "(a + flatbuffers.UOffsetT(j*" +
+        NumToString(InlineSize(vectortype)) + "))");
+    code += "\n\t}\n";
     if (vectortype.base_type == BASE_TYPE_STRING) {
       code += "\treturn nil\n";
     } else if (vectortype.base_type == BASE_TYPE_BOOL) {
@@ -609,7 +655,8 @@ class GoGenerator : public BaseGenerator {
     code += " Mutate" + MakeCamel(field.name);
     code += "(n " + TypeName(field) + ") bool {\n\treturn " + setter;
     code += "(rcv._tab.Pos+flatbuffers.UOffsetT(";
-    code += NumToString(field.value.offset) + "), n)\n}\n\n";
+    code += NumToString(field.value.offset) + "), ";
+    code += CastToBaseType(field.value.type, "n") + ")\n}\n\n";
   }
 
   // Mutate the value of a table's scalar.
@@ -622,7 +669,8 @@ class GoGenerator : public BaseGenerator {
     GenReceiver(struct_def, code_ptr);
     code += " Mutate" + MakeCamel(field.name);
     code += "(n " + TypeName(field) + ") bool {\n\treturn ";
-    code += setter + "(" + NumToString(field.value.offset) + ", n)\n";
+    code += setter + "(" + NumToString(field.value.offset) + ", ";
+    code += CastToBaseType(field.value.type, "n") + ")\n";
     code += "}\n\n";
   }
 
@@ -641,7 +689,8 @@ class GoGenerator : public BaseGenerator {
     code += "\t\ta := rcv._tab.Vector(o)\n";
     code += "\t\treturn " + setter + "(";
     code += "a+flatbuffers.UOffsetT(j*";
-    code += NumToString(InlineSize(vectortype)) + "), n)\n";
+    code += NumToString(InlineSize(vectortype)) + "), ";
+    code += CastToBaseType(vectortype, "n") + ")\n";
     code += "\t}\n";
     code += "\treturn false\n";
     code += "}\n\n";
@@ -726,6 +775,7 @@ class GoGenerator : public BaseGenerator {
   void GenEnum(const EnumDef &enum_def, std::string *code_ptr) {
     if (enum_def.generated) return;
 
+    const int max_name_length = MaxNameLength(enum_def);
     cur_name_space_ = enum_def.defined_namespace;
 
     GenComment(enum_def.doc_comment, code_ptr, nullptr);
@@ -734,16 +784,26 @@ class GoGenerator : public BaseGenerator {
     for (auto it = enum_def.Vals().begin(); it != enum_def.Vals().end(); ++it) {
       auto &ev = **it;
       GenComment(ev.doc_comment, code_ptr, nullptr, "\t");
-      EnumMember(enum_def, ev, code_ptr);
+      EnumMember(enum_def, ev, max_name_length, code_ptr);
     }
     EndEnum(code_ptr);
 
     BeginEnumNames(enum_def, code_ptr);
     for (auto it = enum_def.Vals().begin(); it != enum_def.Vals().end(); ++it) {
       auto &ev = **it;
-      EnumNameMember(enum_def, ev, code_ptr);
+      EnumNameMember(enum_def, ev, max_name_length, code_ptr);
     }
     EndEnumNames(code_ptr);
+
+    BeginEnumValues(enum_def, code_ptr);
+    for (auto it = enum_def.Vals().begin(); it != enum_def.Vals().end();
+         ++it) {
+      auto &ev = **it;
+      EnumValueMember(enum_def, ev, max_name_length, code_ptr);
+    }
+    EndEnumValues(code_ptr);
+
+    EnumStringer(enum_def, code_ptr);
   }
 
   // Returns the function name that is able to read a value of the given type.
@@ -788,7 +848,7 @@ class GoGenerator : public BaseGenerator {
   }
 
   std::string GenTypeGet(const Type &type) {
-    if (type.enum_def != nullptr && !type.enum_def->is_union) {
+    if (type.enum_def != nullptr) {
       return GetEnumTypeName(*type.enum_def);
     }
     return IsScalar(type.base_type) ? GenTypeBasic(type) : GenTypePointer(type);
@@ -798,6 +858,26 @@ class GoGenerator : public BaseGenerator {
     return GenTypeGet(field.value.type);
   }
 
+  // If type is an enum, returns value with a cast to the enum type, otherwise
+  // returns value as-is.
+  std::string CastToEnum(const Type &type, std::string value) {
+    if (type.enum_def == nullptr) {
+      return value;
+    } else {
+      return GenTypeGet(type) + "(" + value + ")";
+    }
+  }
+
+  // If type is an enum, returns value with a cast to the enum base type,
+  // otherwise returns value as-is.
+  std::string CastToBaseType(const Type &type, std::string value) {
+    if (type.enum_def == nullptr) {
+      return value;
+    } else {
+      return GenTypeBasic(type) + "(" + value + ")";
+    }
+  }
+
   std::string GenConstant(const FieldDef &field) {
     switch (field.value.type.base_type) {
       case BASE_TYPE_BOOL: return field.value.constant == "0" ? "false" : "true";;
@@ -816,12 +896,15 @@ class GoGenerator : public BaseGenerator {
   }
   // Begin by declaring namespace and imports.
   void BeginFile(const std::string name_space_name, const bool needs_imports,
-                 std::string *code_ptr) {
+                 const bool is_enum, std::string *code_ptr) {
     std::string &code = *code_ptr;
     code = code + "// Code generated by the FlatBuffers compiler. DO NOT EDIT.\n\n";
     code += "package " + name_space_name + "\n\n";
     if (needs_imports) {
       code += "import (\n";
+      if (is_enum) {
+        code += "\t\"strconv\"\n\n";
+      }
       if (!parser_.opts.go_import.empty()) {
         code += "\tflatbuffers \"" + parser_.opts.go_import + "\"\n";
       } else {
@@ -837,19 +920,27 @@ class GoGenerator : public BaseGenerator {
         }
       }
       code += ")\n\n";
+    } else {
+      if (is_enum) {
+        code += "import \"strconv\"\n\n";
+      }
     }
   }
 
   // Save out the generated code for a Go Table type.
   bool SaveType(const Definition &def, const std::string &classcode,
-                bool needs_imports) {
+                const bool needs_imports, const bool is_enum) {
     if (!classcode.length()) return true;
 
     Namespace &ns = go_namespace_.components.empty() ? *def.defined_namespace
                                                      : go_namespace_;
     std::string code = "";
-    BeginFile(LastNamespacePart(ns), needs_imports, &code);
+    BeginFile(LastNamespacePart(ns), needs_imports, is_enum, &code);
     code += classcode;
+    // Strip extra newlines at end of file to make it gofmt-clean.
+    while (code.length() > 2 && code.substr(code.length() - 2) == "\n\n") {
+      code.pop_back();
+    }
     std::string filename = NamespaceDir(ns) + def.name + ".go";
     return SaveFile(filename.c_str(), code, false);
   }
@@ -897,6 +988,16 @@ class GoGenerator : public BaseGenerator {
   }
 
   const Namespace *CurrentNameSpace() const { return cur_name_space_; }
+
+  static int MaxNameLength(const EnumDef &enum_def) {
+    int max = 0;
+    for (auto it = enum_def.Vals().begin(); it != enum_def.Vals().end();
+        ++it) {
+      const int length = (*it)->name.length();
+      max = length > max ? length : max;
+    }
+    return max;
+  }
 };
 }  // namespace go
 

tests/MyGame/Example/Any.go

@@ -2,7 +2,10 @@
 
 package Example
 
-type Any = byte
+import "strconv"
+
+type Any byte
+
 const (
 	AnyNONE                    Any = 0
 	AnyMonster                 Any = 1
@@ -11,9 +14,22 @@ const (
 )
 
 var EnumNamesAny = map[Any]string{
-	AnyNONE:"NONE",
-	AnyMonster:"Monster",
-	AnyTestSimpleTableWithEnum:"TestSimpleTableWithEnum",
-	AnyMyGame_Example2_Monster:"MyGame_Example2_Monster",
+	AnyNONE:                    "NONE",
+	AnyMonster:                 "Monster",
+	AnyTestSimpleTableWithEnum: "TestSimpleTableWithEnum",
+	AnyMyGame_Example2_Monster: "MyGame_Example2_Monster",
 }
 
+var EnumValuesAny = map[string]Any{
+	"NONE":                    AnyNONE,
+	"Monster":                 AnyMonster,
+	"TestSimpleTableWithEnum": AnyTestSimpleTableWithEnum,
+	"MyGame_Example2_Monster": AnyMyGame_Example2_Monster,
+}
+
+func (v Any) String() string {
+	if s, ok := EnumNamesAny[v]; ok {
+		return s
+	}
+	return "Any(" + strconv.FormatInt(int64(v), 10) + ")"
+}

tests/MyGame/Example/AnyAmbiguousAliases.go

@@ -2,7 +2,10 @@
 
 package Example
 
-type AnyAmbiguousAliases = byte
+import "strconv"
+
+type AnyAmbiguousAliases byte
+
 const (
 	AnyAmbiguousAliasesNONE AnyAmbiguousAliases = 0
 	AnyAmbiguousAliasesM1   AnyAmbiguousAliases = 1
@@ -11,9 +14,22 @@ const (
 )
 
 var EnumNamesAnyAmbiguousAliases = map[AnyAmbiguousAliases]string{
-	AnyAmbiguousAliasesNONE:"NONE",
-	AnyAmbiguousAliasesM1:"M1",
-	AnyAmbiguousAliasesM2:"M2",
-	AnyAmbiguousAliasesM3:"M3",
+	AnyAmbiguousAliasesNONE: "NONE",
+	AnyAmbiguousAliasesM1:   "M1",
+	AnyAmbiguousAliasesM2:   "M2",
+	AnyAmbiguousAliasesM3:   "M3",
 }
 
+var EnumValuesAnyAmbiguousAliases = map[string]AnyAmbiguousAliases{
+	"NONE": AnyAmbiguousAliasesNONE,
+	"M1":   AnyAmbiguousAliasesM1,
+	"M2":   AnyAmbiguousAliasesM2,
+	"M3":   AnyAmbiguousAliasesM3,
+}
+
+func (v AnyAmbiguousAliases) String() string {
+	if s, ok := EnumNamesAnyAmbiguousAliases[v]; ok {
+		return s
+	}
+	return "AnyAmbiguousAliases(" + strconv.FormatInt(int64(v), 10) + ")"
+}

tests/MyGame/Example/AnyUniqueAliases.go

@@ -2,7 +2,10 @@
 
 package Example
 
-type AnyUniqueAliases = byte
+import "strconv"
+
+type AnyUniqueAliases byte
+
 const (
 	AnyUniqueAliasesNONE AnyUniqueAliases = 0
 	AnyUniqueAliasesM    AnyUniqueAliases = 1
@@ -11,9 +14,22 @@ const (
 )
 
 var EnumNamesAnyUniqueAliases = map[AnyUniqueAliases]string{
-	AnyUniqueAliasesNONE:"NONE",
-	AnyUniqueAliasesM:"M",
-	AnyUniqueAliasesT:"T",
-	AnyUniqueAliasesM2:"M2",
+	AnyUniqueAliasesNONE: "NONE",
+	AnyUniqueAliasesM:    "M",
+	AnyUniqueAliasesT:    "T",
+	AnyUniqueAliasesM2:   "M2",
 }
 
+var EnumValuesAnyUniqueAliases = map[string]AnyUniqueAliases{
+	"NONE": AnyUniqueAliasesNONE,
+	"M":    AnyUniqueAliasesM,
+	"T":    AnyUniqueAliasesT,
+	"M2":   AnyUniqueAliasesM2,
+}
+
+func (v AnyUniqueAliases) String() string {
+	if s, ok := EnumNamesAnyUniqueAliases[v]; ok {
+		return s
+	}
+	return "AnyUniqueAliases(" + strconv.FormatInt(int64(v), 10) + ")"
+}

tests/MyGame/Example/Color.go

@@ -2,7 +2,10 @@
 
 package Example
 
-type Color = byte
+import "strconv"
+
+type Color byte
+
 const (
 	ColorRed   Color = 1
 	ColorGreen Color = 2
@@ -10,8 +13,20 @@ const (
 )
 
 var EnumNamesColor = map[Color]string{
-	ColorRed:"Red",
-	ColorGreen:"Green",
-	ColorBlue:"Blue",
+	ColorRed:   "Red",
+	ColorGreen: "Green",
+	ColorBlue:  "Blue",
 }
 
+var EnumValuesColor = map[string]Color{
+	"Red":   ColorRed,
+	"Green": ColorGreen,
+	"Blue":  ColorBlue,
+}
+
+func (v Color) String() string {
+	if s, ok := EnumNamesColor[v]; ok {
+		return s
+	}
+	return "Color(" + strconv.FormatInt(int64(v), 10) + ")"
+}

tests/MyGame/Example/Monster.go

@@ -111,25 +111,25 @@ func (rcv *Monster) MutateInventory(j int, n byte) bool {
 func (rcv *Monster) Color() Color {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(16))
 	if o != 0 {
-		return rcv._tab.GetByte(o + rcv._tab.Pos)
+		return Color(rcv._tab.GetByte(o + rcv._tab.Pos))
 	}
 	return 8
 }
 
 func (rcv *Monster) MutateColor(n Color) bool {
-	return rcv._tab.MutateByteSlot(16, n)
+	return rcv._tab.MutateByteSlot(16, byte(n))
 }
 
-func (rcv *Monster) TestType() byte {
+func (rcv *Monster) TestType() Any {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(18))
 	if o != 0 {
-		return rcv._tab.GetByte(o + rcv._tab.Pos)
+		return Any(rcv._tab.GetByte(o + rcv._tab.Pos))
 	}
 	return 0
 }
 
-func (rcv *Monster) MutateTestType(n byte) bool {
-	return rcv._tab.MutateByteSlot(18, n)
+func (rcv *Monster) MutateTestType(n Any) bool {
+	return rcv._tab.MutateByteSlot(18, byte(n))
 }
 
 func (rcv *Monster) Test(obj *flatbuffers.Table) bool {
@@ -739,16 +739,16 @@ func (rcv *Monster) MutateVectorOfNonOwningReferences(j int, n uint64) bool {
 	return false
 }
 
-func (rcv *Monster) AnyUniqueType() byte {
+func (rcv *Monster) AnyUniqueType() AnyUniqueAliases {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(90))
 	if o != 0 {
-		return rcv._tab.GetByte(o + rcv._tab.Pos)
+		return AnyUniqueAliases(rcv._tab.GetByte(o + rcv._tab.Pos))
 	}
 	return 0
 }
 
-func (rcv *Monster) MutateAnyUniqueType(n byte) bool {
-	return rcv._tab.MutateByteSlot(90, n)
+func (rcv *Monster) MutateAnyUniqueType(n AnyUniqueAliases) bool {
+	return rcv._tab.MutateByteSlot(90, byte(n))
 }
 
 func (rcv *Monster) AnyUnique(obj *flatbuffers.Table) bool {
@@ -760,16 +760,16 @@ func (rcv *Monster) AnyUnique(obj *flatbuffers.Table) bool {
 	return false
 }
 
-func (rcv *Monster) AnyAmbiguousType() byte {
+func (rcv *Monster) AnyAmbiguousType() AnyAmbiguousAliases {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(94))
 	if o != 0 {
-		return rcv._tab.GetByte(o + rcv._tab.Pos)
+		return AnyAmbiguousAliases(rcv._tab.GetByte(o + rcv._tab.Pos))
 	}
 	return 0
 }
 
-func (rcv *Monster) MutateAnyAmbiguousType(n byte) bool {
-	return rcv._tab.MutateByteSlot(94, n)
+func (rcv *Monster) MutateAnyAmbiguousType(n AnyAmbiguousAliases) bool {
+	return rcv._tab.MutateByteSlot(94, byte(n))
 }
 
 func (rcv *Monster) AnyAmbiguous(obj *flatbuffers.Table) bool {
@@ -785,7 +785,7 @@ func (rcv *Monster) VectorOfEnums(j int) Color {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(98))
 	if o != 0 {
 		a := rcv._tab.Vector(o)
-		return rcv._tab.GetByte(a + flatbuffers.UOffsetT(j*1))
+		return Color(rcv._tab.GetByte(a + flatbuffers.UOffsetT(j*1)))
 	}
 	return 0
 }
@@ -810,7 +810,7 @@ func (rcv *Monster) MutateVectorOfEnums(j int, n Color) bool {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(98))
 	if o != 0 {
 		a := rcv._tab.Vector(o)
-		return rcv._tab.MutateByte(a+flatbuffers.UOffsetT(j*1), n)
+		return rcv._tab.MutateByte(a+flatbuffers.UOffsetT(j*1), byte(n))
 	}
 	return false
 }

tests/MyGame/Example/TestSimpleTableWithEnum.go

@@ -29,13 +29,13 @@ func (rcv *TestSimpleTableWithEnum) Table() flatbuffers.Table {
 func (rcv *TestSimpleTableWithEnum) Color() Color {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(4))
 	if o != 0 {
-		return rcv._tab.GetByte(o + rcv._tab.Pos)
+		return Color(rcv._tab.GetByte(o + rcv._tab.Pos))
 	}
 	return 2
 }
 
 func (rcv *TestSimpleTableWithEnum) MutateColor(n Color) bool {
-	return rcv._tab.MutateByteSlot(4, n)
+	return rcv._tab.MutateByteSlot(4, byte(n))
 }
 
 func TestSimpleTableWithEnumStart(builder *flatbuffers.Builder) {

tests/MyGame/Example/Vec3.go

@@ -48,10 +48,10 @@ func (rcv *Vec3) MutateTest1(n float64) bool {
 }
 
 func (rcv *Vec3) Test2() Color {
-	return rcv._tab.GetByte(rcv._tab.Pos + flatbuffers.UOffsetT(24))
+	return Color(rcv._tab.GetByte(rcv._tab.Pos + flatbuffers.UOffsetT(24)))
 }
 func (rcv *Vec3) MutateTest2(n Color) bool {
-	return rcv._tab.MutateByte(rcv._tab.Pos+flatbuffers.UOffsetT(24), n)
+	return rcv._tab.MutateByte(rcv._tab.Pos+flatbuffers.UOffsetT(24), byte(n))
 }
 
 func (rcv *Vec3) Test3(obj *Test) *Test {

tests/go_test.go

@@ -106,6 +106,12 @@ func TestAll(t *testing.T) {
 	// Verify the enum names
 	CheckEnumNames(t.Fatalf)
 
+	// Verify enum String methods
+	CheckEnumString(t.Fatalf)
+
+	// Verify the enum values maps
+	CheckEnumValues(t.Fatalf)
+
 	// Verify that the Go code used in FlatBuffers documentation passes
 	// some sanity checks:
 	CheckDocExample(generated, off, t.Fatalf)
@@ -199,8 +205,8 @@ func CheckReadBuffer(buf []byte, offset flatbuffers.UOffsetT, fail func(string,
 			fail(FailString("Pos.Test1", float64(3.0), got))
 		}
 
-		if got := vec.Test2(); uint8(2) != got {
-			fail(FailString("Pos.Test2", uint8(2), got))
+		if got := vec.Test2(); example.ColorGreen != got {
+			fail(FailString("Pos.Test2", example.ColorGreen, got))
 		}
 
 		// initialize a Test from Test3(...)
@@ -331,7 +337,7 @@ func CheckMutateBuffer(org []byte, offset flatbuffers.UOffsetT, fail func(string
 		testcase{"Pos.Y'", func() bool { return monster.Pos(nil).Y() == float32(2.0) }},
 		testcase{"Pos.Z'", func() bool { return monster.Pos(nil).Z() == float32(3.0) }},
 		testcase{"Pos.Test1'", func() bool { return monster.Pos(nil).Test1() == float64(3.0) }},
-		testcase{"Pos.Test2'", func() bool { return monster.Pos(nil).Test2() == uint8(2) }},
+		testcase{"Pos.Test2'", func() bool { return monster.Pos(nil).Test2() == example.ColorGreen }},
 		testcase{"Pos.Test3.A", func() bool { return monster.Pos(nil).Test3(nil).A() == int16(5) }},
 		testcase{"Pos.Test3.B", func() bool { return monster.Pos(nil).Test3(nil).B() == int8(6) }},
 		testcase{"Inventory[2]", func() bool { return monster.Inventory(2) == byte(2) }},
@@ -345,7 +351,7 @@ func CheckMutateBuffer(org []byte, offset flatbuffers.UOffsetT, fail func(string
 		testcase{"Pos.Y", func() bool { return monster.Pos(nil).MutateY(20.0) }},
 		testcase{"Pos.Z", func() bool { return monster.Pos(nil).MutateZ(30.0) }},
 		testcase{"Pos.Test1", func() bool { return monster.Pos(nil).MutateTest1(30.0) }},
-		testcase{"Pos.Test2", func() bool { return monster.Pos(nil).MutateTest2(20) }},
+		testcase{"Pos.Test2", func() bool { return monster.Pos(nil).MutateTest2(example.ColorBlue) }},
 		testcase{"Pos.Test3.A", func() bool { return monster.Pos(nil).Test3(nil).MutateA(50) }},
 		testcase{"Pos.Test3.B", func() bool { return monster.Pos(nil).Test3(nil).MutateB(60) }},
 		testcase{"Inventory[2]", func() bool { return monster.MutateInventory(2, 200) }},
@@ -359,12 +365,17 @@ func CheckMutateBuffer(org []byte, offset flatbuffers.UOffsetT, fail func(string
 		testcase{"Pos.Y'", func() bool { return monster.Pos(nil).Y() == float32(20.0) }},
 		testcase{"Pos.Z'", func() bool { return monster.Pos(nil).Z() == float32(30.0) }},
 		testcase{"Pos.Test1'", func() bool { return monster.Pos(nil).Test1() == float64(30.0) }},
-		testcase{"Pos.Test2'", func() bool { return monster.Pos(nil).Test2() == uint8(20) }},
+		testcase{"Pos.Test2'", func() bool { return monster.Pos(nil).Test2() == example.ColorBlue }},
 		testcase{"Pos.Test3.A", func() bool { return monster.Pos(nil).Test3(nil).A() == int16(50) }},
 		testcase{"Pos.Test3.B", func() bool { return monster.Pos(nil).Test3(nil).B() == int8(60) }},
 		testcase{"Inventory[2]", func() bool { return monster.Inventory(2) == byte(200) }},
 	}
 
+	testInvalidEnumValues := []testcase{
+		testcase{"Pos.Test2", func() bool { return monster.Pos(nil).MutateTest2(example.Color(20)) }},
+		testcase{"Pos.Test2", func() bool { return monster.Pos(nil).Test2() == example.Color(20) }},
+	}
+
 	// make sure original values are okay
 	for _, t := range testForOriginalValues {
 		if !t.testfn() {
@@ -400,6 +411,14 @@ func CheckMutateBuffer(org []byte, offset flatbuffers.UOffsetT, fail func(string
 		}
 	}
 
+	// a couple extra tests for "invalid" enum values, which don't correspond to
+	// anything in the schema, but are allowed
+	for _, t := range testInvalidEnumValues {
+		if !t.testfn() {
+			fail("field '" + t.field + "' doesn't work with an invalid enum value")
+		}
+	}
+
 	// reverting all fields to original values should
 	// re-create the original buffer. Mutate all fields
 	// back to their original values and compare buffers.
@@ -412,7 +431,7 @@ func CheckMutateBuffer(org []byte, offset flatbuffers.UOffsetT, fail func(string
 	monster.Pos(nil).MutateY(2.0)
 	monster.Pos(nil).MutateZ(3.0)
 	monster.Pos(nil).MutateTest1(3.0)
-	monster.Pos(nil).MutateTest2(2)
+	monster.Pos(nil).MutateTest2(example.ColorGreen)
 	monster.Pos(nil).Test3(nil).MutateA(5)
 	monster.Pos(nil).Test3(nil).MutateB(6)
 	monster.MutateInventory(2, 2)
@@ -1379,7 +1398,6 @@ func CheckFinishedBytesError(fail func(string, ...interface{})) {
 // CheckEnumNames checks that the generated enum names are correct.
 func CheckEnumNames(fail func(string, ...interface{})) {
 	{
-
 		want := map[example.Any]string{
 			example.AnyNONE:                    "NONE",
 			example.AnyMonster:                 "Monster",
@@ -1404,6 +1422,43 @@ func CheckEnumNames(fail func(string, ...interface{})) {
 	}
 }
 
+// CheckEnumString checks the String method on generated enum types.
+func CheckEnumString(fail func(string, ...interface{})) {
+	if got := example.AnyMonster.String(); got != "Monster" {
+		fail("Monster.String: %q != %q", got, "Monster")
+	}
+	if got := fmt.Sprintf("color: %s", example.ColorGreen); got != "color: Green" {
+		fail("color.String: %q != %q", got, "color: Green")
+	}
+}
+
+// CheckEnumValues checks that the generated enum values maps are correct.
+func CheckEnumValues(fail func(string, ...interface{})) {
+	{
+		want := map[string]example.Any{
+			"NONE":                    example.AnyNONE,
+			"Monster":                 example.AnyMonster,
+			"TestSimpleTableWithEnum": example.AnyTestSimpleTableWithEnum,
+			"MyGame_Example2_Monster": example.AnyMyGame_Example2_Monster,
+		}
+		got := example.EnumValuesAny
+		if !reflect.DeepEqual(got, want) {
+			fail("enum name is not equal")
+		}
+	}
+	{
+		want := map[string]example.Color{
+			"Red":   example.ColorRed,
+			"Green": example.ColorGreen,
+			"Blue":  example.ColorBlue,
+		}
+		got := example.EnumValuesColor
+		if !reflect.DeepEqual(got, want) {
+			fail("enum name is not equal")
+		}
+	}
+}
+
 // CheckDocExample checks that the code given in FlatBuffers documentation
 // is syntactically correct.
 func CheckDocExample(buf []byte, off flatbuffers.UOffsetT, fail func(string, ...interface{})) {

tests/namespace_test/NamespaceA/NamespaceB/EnumInNestedNS.go

@@ -2,7 +2,10 @@
 
 package NamespaceB
 
-type EnumInNestedNS = int8
+import "strconv"
+
+type EnumInNestedNS int8
+
 const (
 	EnumInNestedNSA EnumInNestedNS = 0
 	EnumInNestedNSB EnumInNestedNS = 1
@@ -10,8 +13,20 @@ const (
 )
 
 var EnumNamesEnumInNestedNS = map[EnumInNestedNS]string{
-	EnumInNestedNSA:"A",
-	EnumInNestedNSB:"B",
-	EnumInNestedNSC:"C",
+	EnumInNestedNSA: "A",
+	EnumInNestedNSB: "B",
+	EnumInNestedNSC: "C",
 }
 
+var EnumValuesEnumInNestedNS = map[string]EnumInNestedNS{
+	"A": EnumInNestedNSA,
+	"B": EnumInNestedNSB,
+	"C": EnumInNestedNSC,
+}
+
+func (v EnumInNestedNS) String() string {
+	if s, ok := EnumNamesEnumInNestedNS[v]; ok {
+		return s
+	}
+	return "EnumInNestedNS(" + strconv.FormatInt(int64(v), 10) + ")"
+}

tests/namespace_test/NamespaceA/TableInFirstNS.go

@@ -44,13 +44,13 @@ func (rcv *TableInFirstNS) FooTable(obj *NamespaceA__NamespaceB.TableInNestedNS)
 func (rcv *TableInFirstNS) FooEnum() EnumInNestedNS {
 	o := flatbuffers.UOffsetT(rcv._tab.Offset(6))
 	if o != 0 {
-		return rcv._tab.GetInt8(o + rcv._tab.Pos)
+		return EnumInNestedNS(rcv._tab.GetInt8(o + rcv._tab.Pos))
 	}
 	return 0
 }
 
 func (rcv *TableInFirstNS) MutateFooEnum(n EnumInNestedNS) bool {
-	return rcv._tab.MutateInt8Slot(6, n)
+	return rcv._tab.MutateInt8Slot(6, int8(n))
 }
 
 func (rcv *TableInFirstNS) FooStruct(obj *NamespaceA__NamespaceB.StructInNestedNS) *NamespaceA__NamespaceB.StructInNestedNS {