Use BOOST_OVERRIDE to fix GCC -Wsuggest-override and Clang-tidy modernize-use-override warnings.

Also fix Clang-tidy readability-container-size-empty and readability-redundant-string-init warnings.

Author: Eugene Zelenko

include/boost/contract/core/exception.hpp

@@ -1,4 +1,3 @@
-
 #ifndef BOOST_CONTRACT_EXCEPTION_HPP_
 #define BOOST_CONTRACT_EXCEPTION_HPP_
 
@@ -96,16 +95,18 @@ class BOOST_CONTRACT_DETAIL_DECLSPEC bad_virtual_result_cast : // Copy (as str).
 
     @b Throws: This is declared @c noexcept (or @c throw() before C++11).
     */
-    virtual ~bad_virtual_result_cast()
-            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */;
+    ~bad_virtual_result_cast()
+            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */
+            BOOST_OVERRIDE;
 
     /**
     Description for this error (containing both from- and to- type names).
 
     @b Throws: This is declared @c noexcept (or @c throw() before C++11).
     */
-    virtual char const* what() const
-            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */;
+    char const* what() const
+            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */
+            BOOST_OVERRIDE;
 
 /** @cond */
 private:
@@ -166,8 +167,9 @@ class BOOST_CONTRACT_DETAIL_DECLSPEC assertion_failure : // Copy (as str, etc.).
 
     @b Throws: This is declared @c noexcept (or @c throw() before C++11).
     */
-    virtual ~assertion_failure()
-            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */;
+    ~assertion_failure()
+            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */
+            BOOST_OVERRIDE;
 
     /**
     String describing the failed assertion.
@@ -180,8 +182,9 @@ class BOOST_CONTRACT_DETAIL_DECLSPEC assertion_failure : // Copy (as str, etc.).
             File, line, and code will be omitted from this string if they were
             not specified when constructing this object.
     */
-    virtual char const* what() const
-            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */;
+    char const* what() const
+            /** @cond */ BOOST_NOEXCEPT_OR_NOTHROW /** @endcond */
+            BOOST_OVERRIDE;
 
     /**
     Name of the file containing the assertion.
@@ -956,4 +959,3 @@ from_failure_handler const& set_invariant_failure(from_failure_handler const& f)
 } } // namespace
 
 #endif // #include guard
-

include/boost/contract/detail/inlined/core/exception.hpp

@@ -79,9 +79,9 @@ BOOST_CONTRACT_DETAIL_DECLINLINE
 void assertion_failure::init() {
     std::ostringstream text;
     text << "assertion";
-    if(std::string(code_) != "") text << " \"" << code_ << "\"";
+    if(!std::string(code_).empty()) text << " \"" << code_ << "\"";
     text << " failed";
-    if(std::string(file_) != "") {
+    if(!std::string(file_).empty()) {
         text << ": file \"" << file_ << "\"";
         if(line_ != 0) text << ", line " << line_;
     }
@@ -101,7 +101,7 @@ namespace exception_ {
 
     template<failure_key Key>
     void default_handler() {
-        std::string k = "";
+        std::string k;
         switch(Key) {
             case check_failure_key: k = "check "; break;
             case pre_failure_key: k = "precondition "; break;