Having duplicate enumerator values

Question

I'm creating a Tetris clone in C++, and I have an enum GameProperty, which is specified as follows:

enum GameProperty {
    NUM_OF_TETROMINOES  = 7,
    NUM_OF_TILES        = 4,
    TETROMINO_ROTATIONS = 4
};

In my case, I only use these values when looping through a tetromino's tiles, e.g:

for (int i = 0; i < TETROMINO_TILES; i++) { }

Is it under any circumstance considered bad practice to have multiple enumerators with the same value?

Answer 1

These should not be values in a single enum. They should be separate constants. To see why, look at code like i < TETROMINO_TILES. The compares an integer to a GameProperty which can have values like TETROMINO_ROTATIONS. That makes no sense.

Answer 2

Use enum when you want to create a new, distinct type which isn't really a scalar value. For example, colors can be enumerated, and hence numbered, but those numbers don't really mean anything.

If you're assigning meaningful numbers to the enumerators, it's a sign that you might really want something like this:

namespace GameProperty { // completely different concepts with unifying theme
    int const num_tetrominoes  = 7,
              num_tiles        = 4,
              num_rotations    = 4;
};

Now you can use the same syntax, as well as using declarations, and these constants work in for loops and expressions with no conversion.

For another example, the following are both correct but shouldn't be swapped between enum and int:

namespace wavelengths { // closely related quantities
    typedef int wavelength_t; // maybe we will express in-between values
    wavelength_t const red    = 750,
                       green  = 550,
                       blue   = 400;
};

enum colors { // qualitatively different but related as one-of-many
    red,
    green,
    blue;
};

Answer 3

Define a enum just like you define a class. It should conceptually be a collection of values for ONE property, instead of multiple properties rigged up.