Use int as month when constructing date

Question

When I supply an int as an argument to time.Date for month, it works (Example):

time.Date(2016, 1, 1, 0, 0, 0, 0, time.UTC)

Why, when I try to convert a string to int and then use that variable, I get the error:

cannot use mStr (type int) as type time.Month in argument to time.Date

Example: https://play.golang.org/p/-XFNZHK476

Answer 1

You have to convert the value to the proper type:

import(
    "fmt" 
    "time" 
    "strconv"
) 

func main() {
    var m, _ = strconv.Atoi("01")
     // Now convert m to type time.Month 
    fmt.Println(time.Date(2016, time.Month(m), 1, 0, 0, 0, 0, time.UTC))
}

You converted it to a type int, but the 2nd parameter of time.Date() is of type time.Month so it would give you an error that you are not using the correct type.

Answer 2

In the first example you're declaring the type as a time.Month, it is not an int, it is a time.Month. In the second example the type is an int. If you were to do a cast, like in this example it would work as you expect; https://play.golang.org/p/drD_7KiJu4

If in your first example you declared m as an int or just used the := operator (the implied type would be int) and you would get the same error as in the second example. Demonstrated here; https://play.golang.org/p/iWc-2Mpsly

Answer 3

The Go compiler only casts constants to types on its own. Variables need to be explicitly cast.