Private unions (#492)

* changed union of Statement to be private

* changed the union in Expression to be private

* changed union in Value to be private

* changed AST constructors to be static methods

* updates to syntax unit tests

executable_semantics/ast/expression.h

@@ -49,86 +49,104 @@ enum class Operator {
   Sub,
 };
 
+struct Expression;
+
+struct Variable {
+  std::string* name;
+};
+
+struct FieldAccess {
+  const Expression* aggregate;
+  std::string* field;
+};
+
+struct Index {
+  const Expression* aggregate;
+  const Expression* offset;
+};
+
+struct PatternVariable {
+  std::string* name;
+  const Expression* type;
+};
+
+struct Tuple {
+  std::vector<FieldInitializer>* fields;
+};
+
+struct PrimitiveOperator {
+  Operator op;
+  std::vector<const Expression*>* arguments;
+};
+
+struct Call {
+  const Expression* function;
+  const Expression* argument;
+};
+
+struct FunctionType {
+  const Expression* parameter;
+  const Expression* return_type;
+};
+
 struct Expression {
   int line_num;
   ExpressionKind tag;
+
+  static auto MakeVar(int line_num, std::string var) -> const Expression*;
+  static auto MakeVarPat(int line_num, std::string var, const Expression* type)
+      -> const Expression*;
+  static auto MakeInt(int line_num, int i) -> const Expression*;
+  static auto MakeBool(int line_num, bool b) -> const Expression*;
+  static auto MakeOp(int line_num, Operator op,
+                     std::vector<const Expression*>* args) -> const Expression*;
+  static auto MakeUnOp(int line_num, enum Operator op, const Expression* arg)
+      -> const Expression*;
+  static auto MakeBinOp(int line_num, enum Operator op, const Expression* arg1,
+                        const Expression* arg2) -> const Expression*;
+  static auto MakeCall(int line_num, const Expression* fun,
+                       const Expression* arg) -> const Expression*;
+  static auto MakeGetField(int line_num, const Expression* exp,
+                           std::string field) -> const Expression*;
+  static auto MakeTuple(int line_num, std::vector<FieldInitializer>* args)
+      -> const Expression*;
+  static auto MakeUnit(int line_num) -> const Expression*;
+  static auto MakeIndex(int line_num, const Expression* exp,
+                        const Expression* i) -> const Expression*;
+  static auto MakeTypeType(int line_num) -> const Expression*;
+  static auto MakeIntType(int line_num) -> const Expression*;
+  static auto MakeBoolType(int line_num) -> const Expression*;
+  static auto MakeFunType(int line_num, const Expression* param,
+                          const Expression* ret) -> const Expression*;
+  static auto MakeAutoType(int line_num) -> const Expression*;
+  static auto MakeContinuationType(int line_num) -> const Expression*;
+
+  Variable GetVariable() const;
+  FieldAccess GetFieldAccess() const;
+  Index GetIndex() const;
+  PatternVariable GetPatternVariable() const;
+  int GetInteger() const;
+  bool GetBoolean() const;
+  Tuple GetTuple() const;
+  PrimitiveOperator GetPrimitiveOperator() const;
+  Call GetCall() const;
+  FunctionType GetFunctionType() const;
+
+ private:
   union {
-    struct {
-      std::string* name;
-    } variable;
-
-    struct {
-      const Expression* aggregate;
-      std::string* field;
-    } get_field;
-
-    struct {
-      const Expression* aggregate;
-      const Expression* offset;
-    } index;
-
-    struct {
-      std::string* name;
-      const Expression* type;
-    } pattern_variable;
-
+    Variable variable;
+    FieldAccess get_field;
+    Index index;
+    PatternVariable pattern_variable;
     int integer;
     bool boolean;
-
-    struct {
-      std::vector<FieldInitializer>* fields;
-    } tuple;
-
-    struct {
-      Operator op;
-      std::vector<const Expression*>* arguments;
-    } primitive_op;
-
-    struct {
-      const Expression* function;
-      const Expression* argument;
-    } call;
-
-    struct {
-      const Expression* parameter;
-      const Expression* return_type;
-    } function_type;
-
+    Tuple tuple;
+    PrimitiveOperator primitive_op;
+    Call call;
+    FunctionType function_type;
   } u;
 };
 
-auto MakeVar(int line_num, std::string var) -> const Expression*;
-auto MakeVarPat(int line_num, std::string var, const Expression* type)
-    -> const Expression*;
-auto MakeInt(int line_num, int i) -> const Expression*;
-auto MakeBool(int line_num, bool b) -> const Expression*;
-auto MakeOp(int line_num, Operator op, std::vector<const Expression*>* args)
-    -> const Expression*;
-auto MakeUnOp(int line_num, enum Operator op, const Expression* arg)
-    -> const Expression*;
-auto MakeBinOp(int line_num, enum Operator op, const Expression* arg1,
-               const Expression* arg2) -> const Expression*;
-auto MakeCall(int line_num, const Expression* fun, const Expression* arg)
-    -> const Expression*;
-auto MakeGetField(int line_num, const Expression* exp, std::string field)
-    -> const Expression*;
-auto MakeTuple(int line_num, std::vector<FieldInitializer>* args)
-    -> const Expression*;
-// Create an AST node for an empty tuple.
-auto MakeUnit(int line_num) -> const Expression*;
-auto MakeIndex(int line_num, const Expression* exp, const Expression* i)
-    -> const Expression*;
-
-auto MakeTypeType(int line_num) -> const Expression*;
-auto MakeIntType(int line_num) -> const Expression*;
-auto MakeBoolType(int line_num) -> const Expression*;
-auto MakeFunType(int line_num, const Expression* param, const Expression* ret)
-    -> const Expression*;
-auto MakeAutoType(int line_num) -> const Expression*;
-// Returns a Continuation type AST node at the given source location,
-// which is the type of a continuation value.
-auto MakeContinuationType(int line_num) -> const Expression*;
-
 void PrintExp(const Expression* exp);
 
 }  // namespace Carbon