How Can I Skip Iota Values When Assigning Sequential Integers to Constants in Go?

Skipping Constant Values Using Iota in Go

In Go, iota is a special constant used to assign sequential integers to enumerated constants within a constant group. However, there are times when it's necessary to skip assigning iota values to certain constants. Here are three approaches:

Single Group, Manual Offset

If the constants are within the same group, you can manually shift the iota with a constant, leaving empty initialization expressions for those constants you want to skip:

const (
    APPLE = iota
    ORANGE
    PEAR
    BANANA = iota + 96 // 96 is added manually to get 99
    GRAPE
)
fmt.Println(APPLE, ORANGE, PEAR, BANANA, GRAPE)

This approach will produce the desired output: 0, 1, 2, 99, 100. However, changing the order or inserting new constants before BANANA will affect the values of BANANA and subsequent constants.

Breaking the Constant Group

To avoid unexpected value changes, break the constant group and start a new one:

const (
    APPLE = iota
    ORANGE
    PEAR
)

const (
    BANANA = iota + 99 // Iota resets to 0
    GRAPE
)
fmt.Println(APPLE, ORANGE, PEAR, BANANA, GRAPE)

This will also produce the same output, and inserting new constants before BANANA will not affect the values of BANANA and subsequent constants.

Single Group, Automatic Offset

To maintain the single constant group while skipping values, introduce a constant where the break should occur and subtract its value from iota in the next line:

const (
    APPLE = iota
    ORANGE
    PEAR

    _BREAK

    BANANA = iota - _BREAK + 98 // Continues from 98 + 1 = 99
    GRAPE
)
fmt.Println(APPLE, ORANGE, PEAR, BANANA, GRAPE)

This approach ensures that changing the order or inserting new constants before BANANA will not affect the values of BANANA and subsequent constants. To simplify the offset calculation, _BREAK can be initialized with iota 1, so the offset to apply to the next constant is the value of _BREAK itself:

const (
    APPLE = iota
    ORANGE
    PEAR

    _BREAK = iota + 1

    BANANA = iota - _BREAK + 99 // Continues from 99
    GRAPE
)

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