And that's why I hate C++

cclox_src/main.cc

@@ -18,15 +18,13 @@ int main(int argc, char *argv[]) {
   // run_interpreter(argc, argv);
 
   Token unary_op{TokenType::MINUS, "-", Object{}, 1};
-  Expr left_literal = Literal(123);
+  Expr left{unary_op, Expr{123}};
-  Expr left = Unary(unary_op, left_literal.to_expr_ptr());
 
   Token op{TokenType::STAR, "*", Object{}, 1};
 
-  Expr right_literal = Literal(45.67);
+  Expr right{Expr{45.67}, nullptr};
-  Expr right = Grouping(right_literal.to_expr_ptr());
 
-  Expr expr = Binary(left.to_expr_ptr(), op, right.to_expr_ptr());
+  Expr expr{left, op, right};
 
   AstPrinter printer{};
   std::cout << printer.print(expr) << '\n';

cclox_src/parser/expr.cc

@@ -1,42 +1,90 @@
 #include "expr.hh"
 #include "../tokenizer.hh"
 #include <cassert>
+#include <memory>
 #include <string>
+#include <utility>
 #include <vector>
 #include <sstream>
 
+Expr::Expr(const Expr &other) : type{other.type} {
+  switch(type) {
+    case ExprType::BINARY: {
+      std::shared_ptr<Binary> ptr = std::get<std::shared_ptr<Binary>>(other.value);
+      value = std::make_shared<Binary>(*ptr);
+      break;
+    }
+    case ExprType::GROUPING: {
+      std::shared_ptr<Grouping> ptr = std::get<std::shared_ptr<Grouping>>(other.value);
+      value = std::make_shared<Grouping>(*ptr);
+      break;
+    }
+    case ExprType::LITERAL: {
+      std::shared_ptr<Literal> ptr = std::get<std::shared_ptr<Literal>>(other.value);
+      value = std::make_shared<Literal>(*ptr);
+      break;
+    }
+    case ExprType::UNARY: {
+      std::shared_ptr<Unary> ptr = std::get<std::shared_ptr<Unary>>(other.value);
+      value = std::make_shared<Unary>(*ptr);
+      break;
+    }
+  }
+}
+
+// Move constructor
+Expr::Expr(const Expr &&other) : type{other.type}, value{std::move(other.value)} {}
+
+// Binary expressoin
+Expr::Expr(Expr left, Token op, Expr right)
+  : type{ExprType::BINARY}, value{std::make_shared<Binary>(left, op, right)} {}
+
+// Literal expression
+Expr::Expr(Object value)
+  : type{ExprType::LITERAL}, value{std::make_shared<Literal>(value)} {}
+
+// Unary expressoin
+Expr::Expr(Token op, Expr right)
+  : type{ExprType::UNARY}, value{std::make_shared<Unary>(op, right)} {}
+
+// Group expression
+// Has to take an extra parameter to avoid conflicting with copy constructor
+Expr::Expr(Expr expr, void *ptr)
+  : type{ExprType::GROUPING}, value{std::make_shared<Grouping>(expr)} { (void)ptr; }
+
 std::string AstPrinter::print(const Expr &expr) {
   switch (expr.type) {
     case ExprType::BINARY: {
-      _Binary node = std::get<_Binary>(expr.value);
+      std::shared_ptr<Binary> binary = std::get<std::shared_ptr<Binary>>(expr.value);
-      assert(node.left != NULL && node.right != NULL);
+      assert(binary != nullptr);
-      return parenthesize(node.op.lexeme, {*node.left, *node.right});
+      return parenthesize(binary->op.lexeme, {binary->left, binary->right});
     }
     case ExprType::GROUPING: {
-      _Grouping node = std::get<_Grouping>(expr.value);
+      std::shared_ptr<Grouping> group = std::get<std::shared_ptr<Grouping>>(expr.value);
-      assert(node.expression != NULL);
+      assert(group != nullptr);
-      return parenthesize("group", {*node.expression});
+      return parenthesize("group", {group->expr});
     }
     case ExprType::LITERAL: {
-      _Literal node = std::get<_Literal>(expr.value);
+      std::shared_ptr<Literal> literal = std::get<std::shared_ptr<Literal>>(expr.value);
-      switch (node.value.type) {
+      assert(literal != nullptr);
+      switch (literal->value.type) {
         case ObjectType::NIL:
           return "nil";
         case ObjectType::IDENTIFIER:
         case ObjectType::STRING_LIT: {
-          std::string value = std::get<std::string>(node.value.value);
+          std::string value = std::get<std::string>(literal->value.value);
           return value;
         }
         case ObjectType::NUMBER: {
-          double value = std::get<double>(node.value.value);
+          double value = std::get<double>(literal->value.value);
           return std::to_string(value);
         }
       }
     }
     case ExprType::UNARY: {
-      _Unary node = std::get<_Unary>(expr.value);
+      std::shared_ptr<Unary> unary = std::get<std::shared_ptr<Unary>>(expr.value);
-      assert(node.right != NULL);
+      assert(unary != nullptr);
-      return parenthesize(node.op.lexeme, {*node.right});
+      return parenthesize(unary->op.lexeme, {unary->right});
     }
   }
 }

cclox_src/parser/expr.hh

@@ -7,27 +7,10 @@
 #include <variant>
 
 struct Expr;
-
+struct Binary;
-using ExprPtr = std::shared_ptr<Expr>;
+struct Grouping;
-
+struct Literal;
-struct _Binary {
+struct Unary;
-  ExprPtr left;
-  Token op;
-  ExprPtr right;
-};
-
-struct _Grouping {
-  ExprPtr expression;
-};
-
-struct _Literal {
-  Object value;
-};
-
-struct _Unary {
-  Token op;
-  ExprPtr right;
-};
 
 enum class ExprType {
   BINARY,
@@ -36,30 +19,59 @@ enum class ExprType {
   UNARY,
 };
 
-using ExprVariant = std::variant<_Binary, _Grouping, _Literal, _Unary>;
+using ExprVariant = std::variant<
+  std::shared_ptr<Binary>,
+  std::shared_ptr<Grouping>,
+  std::shared_ptr<Literal>,
+  std::shared_ptr<Unary>
+>;
 
 struct Expr {
+  // Copy constructor
+  Expr(const Expr &other);
+
+  // Move constructor
+  Expr(const Expr &&other);
+
+  // Binary expressoin
+  Expr(Expr left, Token op, Expr right);
+
+  // Literal expression
+  Expr(Object value);
+
+  // Unary expressoin
+  Expr(Token op, Expr right);
+
+  // Group expression
+  // Has to take an extra parameter to avoid conflicting with copy constructor
+  Expr(Expr expr, void *ptr);
+
   ExprType type;
   ExprVariant value;
-
-  ExprPtr to_expr_ptr() { return std::make_shared<Expr>(*this); }
 };
 
-inline Expr Binary(ExprPtr left, Token op, ExprPtr right) {
+struct Binary {
-  return Expr{ExprType::BINARY, _Binary{left, op, right}};
+  Binary(Expr left, Token op, Expr right) : left{left}, op{op}, right{right} {}
-}
+  Expr left;
+  Token op;
+  Expr right;
+};
 
-inline Expr Grouping(ExprPtr expr) {
+struct Grouping {
-  return Expr{ExprType::GROUPING, _Grouping{expr}};
+  Grouping(Expr expr) : expr{expr} {}
-}
+  Expr expr;
+};
 
-inline Expr Literal(Object value) {
+struct Literal {
-  return Expr{ExprType::LITERAL, _Literal{value}};
+  Literal(Object value) : value{value} {}
-}
+  Object value;
+};
 
-inline Expr Unary(Token op, ExprPtr right) {
+struct Unary {
-  return Expr{ExprType::UNARY, _Unary{op, right}};
+  Unary(Token op, Expr right) : op{op}, right{right} {}
-}
+  Token op;
+  Expr right;
+};
 
 class AstPrinter {
 public: