No need to store anything separately, it can be stored directly inline.
If you have an Uno, you will need to remove PORTA, or possibly add some on a Mega, however here is the basic principle which can be expanded for PIN and DDR registers too.
Also #define can be used to mask missing ports on different AVR's
static struct{
inline volatile uint8_t &operator []( char i ){
switch( i ){
case 'A': return PORTA;
case 'B': return PORTB;
case 'C': return PORTC;
case 'D': return PORTD;
};
return GPIOR0; //For safety we can return GPIO on error
}
} port;
Access the ports like this:
port[ 'A' ] = 0b11001100;
port[ 'B' ] = port[ 'C' ];
Edit: modified switch 