From a6e129eb12a69607889599cff175eb0bc4ef16bb Mon Sep 17 00:00:00 2001
From: Abdelrahman Said <said.abdelrahman@flawlessai.com>
Date: Sun, 22 Jun 2025 12:39:47 +0100
Subject: [PATCH] Update to reduce copying of expressions

---
 cclox_src/parser/expr.cc | 19 ++++++++++---------
 cclox_src/parser/expr.hh | 14 +++++++-------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/cclox_src/parser/expr.cc b/cclox_src/parser/expr.cc
index 79c0e88..b961da3 100644
--- a/cclox_src/parser/expr.cc
+++ b/cclox_src/parser/expr.cc
@@ -7,6 +7,7 @@
 #include <vector>
 #include <sstream>
 
+// Copy constructor
 Expr::Expr(const Expr &other) : type{other.type} {
   switch(type) {
     case ExprType::BINARY: {
@@ -36,7 +37,7 @@ Expr::Expr(const Expr &other) : type{other.type} {
 Expr::Expr(const Expr &&other) : type{other.type}, value{std::move(other.value)} {}
 
 // Binary expressoin
-Expr::Expr(Expr left, Token op, Expr right)
+Expr::Expr(const Expr &left, Token op, const Expr &right)
   : type{ExprType::BINARY}, value{std::make_shared<Binary>(left, op, right)} {}
 
 // Literal expression
@@ -44,12 +45,12 @@ Expr::Expr(Object value)
   : type{ExprType::LITERAL}, value{std::make_shared<Literal>(value)} {}
 
 // Unary expressoin
-Expr::Expr(Token op, Expr right)
+Expr::Expr(Token op, const 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)
+Expr::Expr(const Expr &expr, void *ptr)
   : type{ExprType::GROUPING}, value{std::make_shared<Grouping>(expr)} { (void)ptr; }
 
 std::string AstPrinter::print(const Expr &expr) {
@@ -57,12 +58,12 @@ std::string AstPrinter::print(const Expr &expr) {
     case ExprType::BINARY: {
       std::shared_ptr<Binary> binary = std::get<std::shared_ptr<Binary>>(expr.value);
       assert(binary != nullptr);
-      return parenthesize(binary->op.lexeme, {binary->left, binary->right});
+      return parenthesize(binary->op.lexeme, {&binary->left, &binary->right});
     }
     case ExprType::GROUPING: {
       std::shared_ptr<Grouping> group = std::get<std::shared_ptr<Grouping>>(expr.value);
       assert(group != nullptr);
-      return parenthesize("group", {group->expr});
+      return parenthesize("group", {&group->expr});
     }
     case ExprType::LITERAL: {
       std::shared_ptr<Literal> literal = std::get<std::shared_ptr<Literal>>(expr.value);
@@ -84,16 +85,16 @@ std::string AstPrinter::print(const Expr &expr) {
     case ExprType::UNARY: {
       std::shared_ptr<Unary> unary = std::get<std::shared_ptr<Unary>>(expr.value);
       assert(unary != nullptr);
-      return parenthesize(unary->op.lexeme, {unary->right});
+      return parenthesize(unary->op.lexeme, {&unary->right});
     }
   }
 }
 
-std::string AstPrinter::parenthesize(const std::string &name, std::vector<Expr> exprs) {
+std::string AstPrinter::parenthesize(const std::string &name, std::vector<const Expr *> exprs) {
   std::stringstream ss{};
   ss << '(' << name;
-  for (auto &expr : exprs) {
-    ss << ' ' << print(expr);
+  for (const Expr *expr : exprs) {
+    ss << ' ' << print(*expr);
   }
   ss << ')';
 
diff --git a/cclox_src/parser/expr.hh b/cclox_src/parser/expr.hh
index cc6ac9d..869eaac 100644
--- a/cclox_src/parser/expr.hh
+++ b/cclox_src/parser/expr.hh
@@ -34,31 +34,31 @@ struct Expr {
   Expr(const Expr &&other);
 
   // Binary expressoin
-  Expr(Expr left, Token op, Expr right);
+  Expr(const Expr &left, Token op, const Expr &right);
 
   // Literal expression
   Expr(Object value);
 
   // Unary expressoin
-  Expr(Token op, Expr right);
+  Expr(Token op, const Expr &right);
 
   // Group expression
   // Has to take an extra parameter to avoid conflicting with copy constructor
-  Expr(Expr expr, void *ptr);
+  Expr(const Expr &expr, void *ptr);
 
   ExprType type;
   ExprVariant value;
 };
 
 struct Binary {
-  Binary(Expr left, Token op, Expr right) : left{left}, op{op}, right{right} {}
+  Binary(const Expr &left, Token op, const Expr &right) : left{left}, op{op}, right{right} {}
   Expr left;
   Token op;
   Expr right;
 };
 
 struct Grouping {
-  Grouping(Expr expr) : expr{expr} {}
+  Grouping(const Expr &expr) : expr{expr} {}
   Expr expr;
 };
 
@@ -68,7 +68,7 @@ struct Literal {
 };
 
 struct Unary {
-  Unary(Token op, Expr right) : op{op}, right{right} {}
+  Unary(Token op, const Expr &right) : op{op}, right{right} {}
   Token op;
   Expr right;
 };
@@ -77,7 +77,7 @@ class AstPrinter {
 public:
   std::string print(const Expr &expr);
 private:
-  std::string parenthesize(const std::string &name, std::vector<Expr> exprs);
+  std::string parenthesize(const std::string &name, std::vector<const Expr *> exprs);
 };
 
 #endif