Refactor FunctionDefinition towards instance methods (#654)

It felt weird to have a `Make` method in this case.

executable_semantics/ast/declaration.cpp

@@ -8,7 +8,7 @@
 
 namespace Carbon {
 
-void FunctionDeclaration::Print() const { PrintFunDef(definition); }
+void FunctionDeclaration::Print() const { definition.Print(); }
 
 void StructDeclaration::Print() const {
   std::cout << "struct " << *definition.name << " {" << std::endl;

executable_semantics/ast/function_definition.cpp

@@ -8,32 +8,18 @@
 
 namespace Carbon {
 
-auto MakeFunDef(int line_num, std::string name, const Expression* ret_type,
-                const Expression* param_pattern, const Statement* body)
-    -> FunctionDefinition {
-  FunctionDefinition f;
-  f.line_num = line_num;
-  f.name = std::move(name);
-  f.return_type = ret_type;
-  f.param_pattern = param_pattern;
-  f.body = body;
-  return f;
-}
-
-void PrintFunDefDepth(const FunctionDefinition& f, int depth) {
-  std::cout << "fn " << f.name << " ";
-  PrintExp(f.param_pattern);
+void FunctionDefinition::PrintDepth(int depth) const {
+  std::cout << "fn " << name << " ";
+  PrintExp(param_pattern);
   std::cout << " -> ";
-  PrintExp(f.return_type);
-  if (f.body) {
+  PrintExp(return_type);
+  if (body) {
     std::cout << " {" << std::endl;
-    PrintStatement(f.body, depth);
+    PrintStatement(body, depth);
     std::cout << std::endl << "}" << std::endl;
   } else {
     std::cout << ";" << std::endl;
   }
 }
 
-void PrintFunDef(const FunctionDefinition& f) { PrintFunDefDepth(f, -1); }
-
 }  // namespace Carbon

executable_semantics/ast/function_definition.h

@@ -11,6 +11,19 @@
 namespace Carbon {
 
 struct FunctionDefinition {
+  FunctionDefinition() = default;
+  FunctionDefinition(int line_num, std::string name,
+                     const Expression* param_pattern,
+                     const Expression* return_type, const Statement* body)
+      : line_num(line_num),
+        name(std::move(name)),
+        param_pattern(param_pattern),
+        return_type(return_type),
+        body(body) {}
+
+  void Print() const { PrintDepth(-1); }
+  void PrintDepth(int depth) const;
+
   int line_num;
   std::string name;
   const Expression* param_pattern;
@@ -18,12 +31,6 @@ struct FunctionDefinition {
   const Statement* body;
 };
 
-auto MakeFunDef(int line_num, std::string name, const Expression* ret_type,
-                const Expression* param, const Statement* body)
-    -> FunctionDefinition;
-void PrintFunDef(const FunctionDefinition&);
-void PrintFunDefDepth(const FunctionDefinition&, int);
-
 }  // namespace Carbon
 
 #endif  // EXECUTABLE_SEMANTICS_AST_FUNCTION_DEFINITION_H_