diff --git a/src/commands.cc b/src/commands.cc
index 488c892f..c31b99c3 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -242,9 +242,9 @@ void edit(const CommandParameters& params, const Context& context)
 
     if (params.size() > 1)
     {
-        int line = std::max(0, atoi(params[1].c_str()) - 1);
+        int line = std::max(0, str_to_int(params[1]) - 1);
         int column = params.size() > 2 ?
-                         std::max(0, atoi(params[2].c_str()) - 1) : 0;
+                         std::max(0, str_to_int(params[2]) - 1) : 0;
 
         window.select(window.buffer().iterator_at({line, column}));
     }
@@ -473,7 +473,7 @@ EnvVarMap params_to_env_var_map(const CommandParameters& params)
     for (size_t i = 0; i < params.size(); ++i)
     {
          param_name[sizeof(param_name) - 2] = '0' + i;
-         vars[param_name] = params[i].c_str();
+         vars[param_name] = params[i];
     }
     return vars;
 }
@@ -567,7 +567,7 @@ void exec_commands_in_file(const CommandParameters& params,
     while (true)
     {
          if (not cat_with_previous)
-             command_line.clear();
+             command_line = String();
 
          size_t end_pos = pos;
 
@@ -796,7 +796,7 @@ void menu(const CommandParameters& params,
     oss << "(empty cancels): ";
 
     String choice = prompt(oss.str(), complete_nothing);
-    int i = atoi(choice.c_str());
+    int i = str_to_int(choice);
 
     if (i > 0 and i < (count / 2) + 1)
         CommandManager::instance().execute(parser[(i-1)*2+1], context);
diff --git a/src/filters.cc b/src/filters.cc
index 185dd1bf..d7cb7fdf 100644
--- a/src/filters.cc
+++ b/src/filters.cc
@@ -57,7 +57,7 @@ void expand_tabulations(Buffer& buffer, Modification& modification)
         }
 
         int count = tabstop - (column % tabstop);
-        modification.content.clear();
+        modification.content = String();
         for (int i = 0; i < count; ++i)
             modification.content += ' ';
     }
diff --git a/src/option_manager.hh b/src/option_manager.hh
index 49b8c9d5..f6d21bd2 100644
--- a/src/option_manager.hh
+++ b/src/option_manager.hh
@@ -31,7 +31,7 @@ public:
     bool operator==(const Option& other) const { return m_value == other.m_value; }
     bool operator!=(const Option& other) const { return m_value != other.m_value; }
 
-    int    as_int()    const  { return atoi(m_value.c_str()); }
+    int    as_int()    const  { return str_to_int(m_value); }
     String as_string() const { return m_value; }
 private:
     String m_value;
diff --git a/src/string.cc b/src/string.cc
index 30654256..9e2d1507 100644
--- a/src/string.cc
+++ b/src/string.cc
@@ -25,6 +25,11 @@ String int_to_str(int value)
     return String(buffer + pos);
 }
 
+int str_to_int(const String& str)
+{
+    return atoi(str.c_str());
+}
+
 std::vector<String> split(const String& str, Character separator)
 {
     auto begin = str.begin();
diff --git a/src/string.hh b/src/string.hh
index 0a8c0abb..cd5cfe1d 100644
--- a/src/string.hh
+++ b/src/string.hh
@@ -16,7 +16,9 @@ class String
 public:
    String() {}
    String(const char* content) : m_content(content) {}
-   String(const std::string& content) : m_content(content) {}
+   String(std::string content) : m_content(std::move(content)) {}
+   String(const String& string) = default;
+   String(String&& string) = default;
    explicit String(Character content) : m_content(std::string() + (char)content) {}
    template<typename Iterator>
    String(Iterator begin, Iterator end) : m_content(begin, end) {}
@@ -30,6 +32,7 @@ public:
    bool      operator<  (const String& other) const { return m_content < other.m_content;  }
 
    String&   operator=  (const String& other)       { m_content = other.m_content; return *this; }
+   String&   operator=  (String&& other)            { m_content = std::move(other.m_content); return *this; }
 
    String    operator+  (const String& other) const { return String(m_content + other.m_content); }
    String&   operator+= (const String& other)       { m_content += other.m_content; return *this; }
@@ -41,7 +44,6 @@ public:
    const char*      c_str() const { return m_content.c_str(); }
 
    String substr(size_t pos, size_t length = -1) const { return String(m_content.substr(pos, length)); }
-   void   clear() { m_content.clear(); }
 
    class iterator
    {
@@ -110,6 +112,7 @@ inline String operator+(Character lhs, const String& rhs)
 }
 
 String int_to_str(int value);
+int    str_to_int(const String& str);
 std::vector<String> split(const String& str, Character separator);
 
 }