StringHashMap.cpp

std::vector<std::string> someFunction( const Invocation& invocation )
{
	// Define hash and comparison for string pointers, by value
	struct StringPtrTraits
	{
		size_t operator()( const std::string* rsi ) const
		{
			return std::hash<std::string>()( *rsi );
		}
		bool operator()( const std::string* a, const std::string* b ) const
		{
			return ( *a == *b );
		}
	};
	using TagsCollection = std::unordered_set<const std::string*, StringPtrTraits, StringPtrTraits>;
	TagsCollection tags;

	// Add input strings to the hash set
	// This loop doesn't copy any strings, the hash set references the original pointers
	for( const auto& error : invocation.errors() )
		for( const std::string& s : error.tags() )
			tags.insert( &s );

	// And here we make copies
	std::vector<std::string> result;
	result.reserve( tags.size() );
	for( const std::string* e : tags )
		result.push_back( *e );
	return result;
}