`math/rand/v2`

Guided tour · Math · pkg.go.dev →

Pseudo-random numbers (Go 1.22+). Auto-seeded, simpler API, and not safe for cryptographic use — reach for crypto/rand for that.

v2 vs v1

math/rand/v2 is a cleaner redo. No more manual seeding, no global mutex bottleneck on concurrent use, and a tighter API. Prefer v2 for new code.

IntN(n) returns a number in [0, n). Float64() returns [0.0, 1.0).

rand.IntN(6) + 1          // dice roll 1..6
rand.Float64()            // [0, 1)
rand.Int32()              // full range int32
rand.Uint64()

d := rand.N(6) + 1        // returns int, [0, 6)
t := rand.N(10 * time.Second)  // random duration up to 10s

xs := []int{1, 2, 3, 4, 5}
rand.Shuffle(len(xs), func(i, j int) {
    xs[i], xs[j] = xs[j], xs[i]
})

order := rand.Perm(5)   // e.g., [3 0 4 1 2]

Use this in tests. The default global rand is seeded randomly per process — good for production, bad for assertions.

r := rand.New(rand.NewPCG(1, 2))
for i := 0; i < 3; i++ {
    fmt.Println(r.IntN(100))
}