From 1075c3ca262d4b31949ac42f89984d8bae1c2754 Mon Sep 17 00:00:00 2001
From: Theodore Chang <tlcfem@gmail.com>
Date: Wed, 20 Nov 2024 22:06:31 +0100
Subject: [PATCH] Pass `std::string_view` by value

---
 Toolbox/Expression.cpp | 6 +++---
 Toolbox/Expression.h   | 6 +++---
 Toolbox/utility.cpp    | 2 +-
 Toolbox/utility.h      | 2 +-
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/Toolbox/Expression.cpp b/Toolbox/Expression.cpp
index 84df06356..a9430fb63 100644
--- a/Toolbox/Expression.cpp
+++ b/Toolbox/Expression.cpp
@@ -43,7 +43,7 @@ uword Expression::input_size() const { return x.n_elem; }
 
 uword Expression::output_size() const { return 1; }
 
-bool Expression::compile(const std::string_view& expression_string) {
+bool Expression::compile(const std::string_view expression_string) {
     expression.register_symbol_table(symbol_table);
     std::scoped_lock lock{parser_mutex};
     return parser.compile(expression_text = expression_string, expression);
@@ -59,7 +59,7 @@ void Expression::print() {
     suanpan_info("An expression represents \"{}\".", expression_text);
 }
 
-SimpleScalarExpression::SimpleScalarExpression(const unsigned tag, const std::string_view& input_string)
+SimpleScalarExpression::SimpleScalarExpression(const unsigned tag, const std::string_view input_string)
     : Expression(tag, {std::string{input_string}}) {}
 
 unique_ptr<Expression> SimpleScalarExpression::get_copy() const {
@@ -84,7 +84,7 @@ Mat<double> SimpleScalarExpression::gradient(const Col<double>& in_x) {
     return result;
 }
 
-SimpleVectorExpression::SimpleVectorExpression(const unsigned tag, const std::string_view& input_string, const std::string_view& output_string)
+SimpleVectorExpression::SimpleVectorExpression(const unsigned tag, const std::string_view input_string, const std::string_view output_string)
     : Expression(tag, {std::string{input_string}, std::string{output_string}}) {
     const auto variable_list = suanpan::expression::split(variable_text_list[1]);
 
diff --git a/Toolbox/Expression.h b/Toolbox/Expression.h
index 2869685e2..d955b7816 100644
--- a/Toolbox/Expression.h
+++ b/Toolbox/Expression.h
@@ -59,7 +59,7 @@ class Expression : public Tag {
     [[nodiscard]] virtual uword input_size() const;
     [[nodiscard]] virtual uword output_size() const;
 
-    bool compile(const std::string_view&);
+    bool compile(std::string_view);
     static std::string error();
 
     Mat<double> evaluate(double);
@@ -73,7 +73,7 @@ class Expression : public Tag {
 
 class SimpleScalarExpression final : public Expression {
 public:
-    SimpleScalarExpression(unsigned, const std::string_view&);
+    SimpleScalarExpression(unsigned, std::string_view);
 
     [[nodiscard]] unique_ptr<Expression> get_copy() const override;
 
@@ -86,7 +86,7 @@ class SimpleVectorExpression final : public Expression {
     Col<double> y;
 
 public:
-    SimpleVectorExpression(unsigned, const std::string_view&, const std::string_view&);
+    SimpleVectorExpression(unsigned, std::string_view, std::string_view);
 
     [[nodiscard]] unique_ptr<Expression> get_copy() const override;
 
diff --git a/Toolbox/utility.cpp b/Toolbox/utility.cpp
index ba2fed804..f07b13a58 100644
--- a/Toolbox/utility.cpp
+++ b/Toolbox/utility.cpp
@@ -66,7 +66,7 @@ string suanpan::to_lower(string&& U) {
     return std::move(U);
 }
 
-std::vector<std::pair<string, unsigned>> suanpan::expression::split(const std::string_view& variable_string) {
+std::vector<std::pair<string, unsigned>> suanpan::expression::split(const std::string_view variable_string) {
     std::vector<std::string> variable_list;
     auto I = variable_string.cbegin(), J = variable_string.cbegin();
     while(I != variable_string.cend()) {
diff --git a/Toolbox/utility.h b/Toolbox/utility.h
index ae3eebfbc..2b93f59df 100644
--- a/Toolbox/utility.h
+++ b/Toolbox/utility.h
@@ -72,7 +72,7 @@ namespace suanpan {
     string to_lower(string&&);
 
     namespace expression {
-        std::vector<std::pair<string, unsigned>> split(const std::string_view& variable_string);
+        std::vector<std::pair<string, unsigned>> split(std::string_view variable_string);
     } // namespace expression 
 }     // namespace suanpan