Why Does Go's `rand.Intn` Sometimes Return the Same Value?

Understanding Discrepancies in Go's rand.Intn Function

When utilizing Go's rand.Intn(n) function to generate a random number within the range [0, n-1], programmers may encounter surprising behavior where the same value is returned consistently. To delve into the reasons behind this issue, let's examine two critical factors:

Initialization of the Random Number Generator (RNG)

Go's rand package leverages a global source to generate random numbers. By default, this source produces a deterministic sequence of values upon every program execution. To customize this behavior and achieve randomness, it's crucial to initialize the default source using rand.Seed(). A common practice is to seed the generator with the current Unix timestamp, like so:

rand.Seed(time.Now().UnixNano())

Caching on the Go Playground

The Go Playground, an online tool for executing Go code, caches its output to enhance performance. Unfortunately, this caching can interfere with the generation of random numbers. Consequently, when running rand.Intn(n) multiple times on the Playground, the same value may be returned repeatedly due to the cached results.

Therefore, to ensure true randomness and avoid repeated values, it's essential to initialize the RNG appropriately and be aware of the caching limitations of the Go Playground.

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