The
bitSizeargument specifies the integer type that the result must fit into
This means the int64 result can be safely casted to your integer type:
i64, _ := strconv.ParseInt("42", 10, 64)
or
i64, _ := strconv.ParseInt("42", 10, 32)
var i32 int32 = i64 // cast to int32
or
i64, _ := strconv.ParseInt("42", 10, 0)
var i int = i64 // cast to int
int is either int32 or int64 depending on your system. With the bitSize 0 you make ParseInt choose the right type for you (32 or 64).