Why Does Go's `rand.Intn()` Return the Same Number?

Go rand.Intn Returns the Same Number

In Go, the rand.Intn() function generates a pseudorandom integer between 0 (inclusive) and n (exclusive). However, users have reported that their code using this function always returns the same value. Why is this happening?

There are two primary reasons for this behavior:

1. Lack of Initialization:
   The rand package maintains a global Source that underlies all its random number generators, including rand.Intn(). By default, this Source is uninitialized, resulting in a deterministic sequence of values. To fix this, call rand.Seed() to initialize the Source with a random value, typically obtained from the system clock:

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

2. Playground Caching:
   For this specific example from the Go tour, the code is run on the Go Playground. The Playground caches its output for performance reasons. This means that even if you generate multiple random numbers, the Playground will show only the first number unless you reload the page.

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