Make StringRef's operator std::string explicit

This way it is explicit when there is a `StringRef` -> `std::string`
conversion and makes it easier to look for allocations that could
be avoided.

Doing this has already removed one allocation per registered test
case, as there was a completely pointless `StringRef` -> `std::string`
conversion when parsing tags of a test case.

include/internal/catch_assertionresult.cpp

@@ -56,13 +56,13 @@ namespace Catch {
         if( isFalseTest( m_info.resultDisposition ) )
             return "!(" + m_info.capturedExpression + ")";
         else
-            return m_info.capturedExpression;
+            return static_cast<std::string>(m_info.capturedExpression);
     }
 
     std::string AssertionResult::getExpressionInMacro() const {
         std::string expr;
         if( m_info.macroName[0] == 0 )
-            expr = m_info.capturedExpression;
+            expr = static_cast<std::string>(m_info.capturedExpression);
         else {
             expr.reserve( m_info.macroName.size() + m_info.capturedExpression.size() + 4 );
             expr += m_info.macroName;

include/internal/catch_message.cpp

@@ -113,7 +113,7 @@ namespace Catch {
             case ',':
                 if (start != pos && openings.size() == 0) {
                     m_messages.emplace_back(macroName, lineInfo, resultType);
-                    m_messages.back().message = trimmed(start, pos);
+                    m_messages.back().message = static_cast<std::string>(trimmed(start, pos));
                     m_messages.back().message += " := ";
                     start = pos;
                 }
@@ -121,7 +121,7 @@ namespace Catch {
         }
         assert(openings.size() == 0 && "Mismatched openings");
         m_messages.emplace_back(macroName, lineInfo, resultType);
-        m_messages.back().message = trimmed(start, names.size() - 1);
+        m_messages.back().message = static_cast<std::string>(trimmed(start, names.size() - 1));
         m_messages.back().message += " := ";
     }
     Capturer::~Capturer() {

include/internal/catch_run_context.cpp

@@ -230,7 +230,7 @@ namespace Catch {
 
         m_unfinishedSections.push_back(endInfo);
     }
-	
+
 #if defined(CATCH_CONFIG_ENABLE_BENCHMARKING)
     void RunContext::benchmarkPreparing(std::string const& name) {
 		m_reporter->benchmarkPreparing(name);
@@ -279,7 +279,7 @@ namespace Catch {
         // Don't rebuild the result -- the stringification itself can cause more fatal errors
         // Instead, fake a result data.
         AssertionResultData tempResult( ResultWas::FatalErrorCondition, { false } );
-        tempResult.message = message;
+        tempResult.message = static_cast<std::string>(message);
         AssertionResult result(m_lastAssertionInfo, tempResult);
 
         assertionEnded(result);
@@ -442,7 +442,7 @@ namespace Catch {
         m_lastAssertionInfo = info;
 
         AssertionResultData data( resultType, LazyExpression( false ) );
-        data.message = message;
+        data.message = static_cast<std::string>(message);
         AssertionResult assertionResult{ m_lastAssertionInfo, data };
         assertionEnded( assertionResult );
         if( !assertionResult.isOk() )

include/internal/catch_stringref.h

@@ -23,6 +23,7 @@ namespace Catch {
     class StringRef {
     public:
         using size_type = std::size_t;
+        using const_iterator = const char*;
 
     private:
         friend struct StringRefTestAccess;
@@ -78,7 +79,7 @@ namespace Catch {
             return *this;
         }
 
-        operator std::string() const;
+        explicit operator std::string() const;
 
         void swap( StringRef& other ) noexcept;
 
@@ -105,6 +106,10 @@ namespace Catch {
         // Note that the pointer can change when if the StringRef is a substring
         auto currentData() const noexcept -> char const*;
 
+    public: // iterators
+        const_iterator begin() const { return m_start; }
+        const_iterator end() const { return m_start + m_size; }
+
     private: // ownership queries - may not be consistent between calls
         auto isOwned() const noexcept -> bool;
         auto isSubstring() const noexcept -> bool;

include/internal/catch_test_case_info.cpp

@@ -59,8 +59,7 @@ namespace Catch {
         std::vector<std::string> tags;
         std::string desc, tag;
         bool inTag = false;
-        std::string _descOrTags = nameAndTags.tags;
-        for (char c : _descOrTags) {
+        for (char c : nameAndTags.tags) {
             if( !inTag ) {
                 if( c == '[' )
                     inTag = true;
@@ -93,7 +92,7 @@ namespace Catch {
             tags.push_back( "." );
         }
 
-        TestCaseInfo info( nameAndTags.name, _className, desc, tags, _lineInfo );
+        TestCaseInfo info( static_cast<std::string>(nameAndTags.name), _className, desc, tags, _lineInfo );
         return TestCase( _testCase, std::move(info) );
     }
 

include/internal/catch_test_case_registry_impl.cpp

@@ -105,7 +105,7 @@ namespace Catch {
     }
 
     std::string extractClassName( StringRef const& classOrQualifiedMethodName ) {
-        std::string className = classOrQualifiedMethodName;
+        std::string className(classOrQualifiedMethodName);
         if( startsWith( className, '&' ) )
         {
             std::size_t lastColons = className.rfind( "::" );

include/internal/catch_tostring.h

@@ -654,7 +654,7 @@ namespace Catch { \
     template<> struct StringMaker<enumName> { \
         static std::string convert( enumName value ) { \
             static const auto& enumInfo = ::Catch::getMutableRegistryHub().getMutableEnumValuesRegistry().registerEnum( #enumName, #__VA_ARGS__, { __VA_ARGS__ } ); \
-            return enumInfo.lookup( static_cast<int>( value ) ); \
+            return static_cast<std::string>(enumInfo.lookup( static_cast<int>( value ) )); \
         } \
     }; \
 }