带范围夹紧的typedef

Question

In Go we can say:

type Month int

to create a new type based off of int.

Is it possible to also say that the range of values allowed for this type is 1 - 12, and to guarantee that no value < 1 or > 12 can be assigned?

Answer 1

No, you cannot put limits on an int whether you define it as a custom type or not. The closest you can get is something like the following code using a construct called iota

type Month int

const (
    Jan Month = iota + 1
    Feb
    Mar
    Apr
    May
    Jun
    Jul
    Aug
    Sep
    Oct
    Nov
    Dec
)

func main() {
    fmt.Println(Jan, Feb, Mar)
}

This will print 1 2 3. There are a lot more uses for it, you can look up more information here https://splice.com/blog/iota-elegant-constants-golang/

This does not guarantee that you cannot assign random values to the resulting variable, but as long as you use the defined constants everywhere you should be fine.