Performance improvements of a method which check if a string is an ANSI escape sequence?-CodePudding

Let's suppose I have a class with a private method is_escape which check if an input string is and ANSI escape sequence. This method is then used in another public method, into an if/else condition:

#include <string>

enum class ANSI { first, generic };

template <class T_str>
class foo
 {
  private:
   template <typename T>
   static constexpr bool is_escape( const T& str, ANSI&& flag ) { /* implementation */ }

  public:
   template <class T>
   void public_method( T str ) // T can be also an int, double etc...
    {
     if ( is_escape( str ) ) { /* do something */ }
    }
 };

The implementation of the is_escape method is the following:

#include <string>
#include <type_traits>

template <typename T>
static constexpr bool is_escape( const T& str, ANSI&& flag )
 {
  if constexpr( std::is_convertible_v <T, std::basic_string_view<T_str>> && ! std::is_same_v<T, std::nullptr_t> )
   {
    switch( flag )
     {
      case( ANSI::first ): 
       {
        return ( ! std::basic_string_view<T_str>( str ).rfind( "\033"s, 0 ) ) && 
               ( std::basic_string_view<T_str>( str ).length() < 7 );
       }
      case( ANSI::generic ):
       {
        return ( std::basic_string_view<T_str>( str ).find( "\033"s ) != std::basic_string_view<T_str>::npos );
       }
     }
   }
  return false;
 }

Is there a better way to write the method in order to improve its performances (in C 17)? Thanks.

CodePudding user response：

At the end, I improved the performances of the function with this signature:

template <typename T>
static constexpr bool is_escape( const T& str, const ANSI& flag )
 {
  if constexpr( std::is_convertible_v <T, std::basic_string_view<T_str>> && ! std::is_same_v<T, std::nullptr_t> )
   {
    switch( flag )
     {
      case( ANSI::first ): 
       {
        return ( std::basic_string_view<T_str>( str ).length() < 7 ) && ( str[0] == '\033' );
       }
      case( ANSI::generic ):
       {
        return ( std::basic_string_view<T_str>( str ).find( '\033' ) != std::basic_string_view<T_str>::npos );
       }
     }
   }
  return false;
 }