Overloading increment operator, looping, and edge cases.

Question

Hello!

I have an enum, that looks like this:

enum Suit {Clubs, Diamonds, Hearts, Spades};

I want to overload the increment operator, so I can easily loop over these four dudes.

When the variable is Clubs, Diamonds, or Hearts there no issue. Its the Spades condition that is giving me a little trouble.

My first instinct was to define it so that when the variable is spades, incrementation sets it equal to Clubs. The problem is that this seems to make it impossible to loop over the 4 values in the enum.

If I do something like

for(Suit i=Clubs;i<Spades;++i)
     {cout<<i<<endl;}

then my output only goes to Hearts.

If i do

for(suit i=Clubs;i<=Spades;++i)
    {cout<<i<<endl;}

then my output just loops forever!

So, I can obviously think of a few workarounds for this... I'm just not sure what the idiomatic C++ thing do to.

Should I redefine incrementation so that attempting to increment a Spade results in a Spade? or maybe throws an exception?

To reiterate: I can definitely think of a few hacky ways to fix this issue. I just want the guidance of experienced programmers to tell me what they think would be the most "normal" way to solve the problem.

Answer 1

You could add enum values for start and termination conditions, and an alternative to ++ which doesn't cycle back to the beginning.

enum Suit { FirstSuit, Clubs = FirstSuit, Diamonds, Hearts, Spades, AllSuits };

for ( suit i = FirstSuit; i != AllSuits; i = iterate_suits( i ) )

Since for and while loops always check the condition before executing, there is no way to end their execution in the middle of a cyclic range without additional variables or flow control. A do while loop works best in this case.

Suit iter_suit = my_suit; // iterate over all suits beginning with my_suit.
do {
} while ( ++ iter_suit != my_suit );

In this case, you don't need FirstSuit and AllSuits.

Answer 2

Perhaps

enum Suit {Clubs, Diamonds, Hearts, Spades, NumberOfSuits};

for(Suit i=Clubs;i<NumberOfSuits;++i)
 {cout<<i<<endl;}

There's still something unidiomatic (I have to know that Clubs is the first suit).

Why not just use the implicit conversion to int?

for (int i = 0; i < NumberOfSuits; ++i)

Answer 3

As suggested in a comment, what about just defining your enum as:

enum Suit {Clubs, Diamonds, Hearts, Spades, EndSuit};

Then your loop becomes:

for(Suit i=Clubs;i<EndSuit;++i)
{
    cout<<i<<endl;
}

Answer 4

Since enum values decay into (unsigned) integers, you could use moduluo arithmetic and then cast back to an enum:

enum Suite add(const enum Suite card1, const enum Suite card 2)
{
 unsigned int result = card1;
 result += card2;
 result = result % 4;
 return (enum Suite) result;  // Casting shown for readability.
}

Suggestion: Make this into a class. With a class you can also add "print" and "input" methods.