About rand.Seed()

As of Go 1.20, there is no reason for calling rand.Seed() using a random value to initiate the random number generator. However, using rand.Seed() is not going to break existing code. To get a specific sequence of numbers, it is recommended to call New(NewSource(seed)) instead.

This is illustrated in ch15/randSeed.go—the relevant Go code is the following:

    src := rand.NewSource(seed)
    r := rand.New(src)
    for i := 0; i < times; i++ {
        fmt.Println(r.Uint64())
    }

The rand.NewSource() call returns a new (pseudo) random source based on the given seed. Therefore, if called with the same seed, it is going to return the same sequence of values. The rand.New() call returns a new *rand.Rand variable, which is what generates the (pseudo) random values. Due to the call to Uint64(), we are generating unsigned int64 values.

Running randSeed.go produces the following output:

$ go run randSeed.go 1
Using seed: 1
5577006791947779410...