Random (Animal Magic) missing hint about difference of slices with string literals vs strings on the heap

[woeps]

I tried to implement ShuffleAnimals

go/exercises/concept/animal-magic/animal_magic.go

Lines 13 to 16 in 26635e1

	// ShuffleAnimals returns a slice with all eight animal strings in random order.
	func ShuffleAnimals() []string {
	panic("Please implement the ShuffleAnimals function")
	}

like this:

// ShuffleAnimals returns a slice with all eight animal strings in random order.
var animals = []string{"ant", "beaver", "cat", "dog", "elephant", "fox", "giraffe", "hedgehog"}
func ShuffleAnimals() []string {
	rand.Shuffle(len(animals), func(i, j int) {
		animals[i], animals[j] = animals[j], animals[i]
	})
	return animals
}

This consistently produced the following error when running tests:

$ go test
--- FAIL: TestShuffleAnimals (0.00s)
    animal_magic_test.go:85: ShuffleAnimals() always generates the same slice: [cat beaver giraffe fox ant
 elephant dog hedgehog]
FAIL
exit status 1
FAIL    chance  0.007s

I smashed my head against the wall for about an hour to solve this. I partially got mislead by the readme's chapter on seeds, which has nothing to do with the solution or the problem I hit:

go/exercises/concept/animal-magic/.docs/introduction.md

Lines 27 to 39 in 26635e1

	## Seeds
	The number sequences generated by package `math/rand` are not truly random.
	Given a specific "seed" value, the results are entirely deterministic.
	In Go 1.20+ the seed is automatically picked at random so you will see a different sequence of random numbers each time you run your program.
	In prior versions of Go, the seed was `1` by default.
	So to get different sequences for various runs of the program, you had to manually seed the random number generator, e.g. with the current time, before retrieving any random numbers.
	```go
	rand.Seed(time.Now().UnixNano())
	```

Doing lots of search and digging more into the rand.Shuffle implementation I learned, that the function's behavior depends on the slice-elements' memory-address: A slice of string literals having constant memory addresses will result in a constant order by rand.Shuffle.

Previous concepts didn't mention differences of string literals vs heap allocated strings and I didn't know about this, which cost me some time and a lot of nerves.

Is it possible to ...

• detect the usage of string literals in the test and print a distinct error?
• add a hint about string literals?
• cover this detail in previous concepts?

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