各个整数类型的 Max Min 值
The germane part:
Since integer types use two's complement arithmetic, you can infer the min/max constant values for int and uint. For example,
const MaxUint = ^uint(0) // 异或运算
const MinUint = 0
const MaxInt = int(MaxUint >> 1) // 干掉符号位
const MinInt = -MaxInt - 1
uint8 : 0 to 255
uint16 : 0 to 65535
uint32 : 0 to 4294967295
uint64 : 0 to 18446744073709551615
int8 : -128 to 127
int16 : -32768 to 32767
int32 : -2147483648 to 2147483647
int64 : -9223372036854775808 to 9223372036854775807