Go: What is the difference between nil and empty slice?

Nil slice — zero value, no backing array. Empty slice — has backing array but no elements.

Both support len, cap, range, and append identically. The difference shows in JSON and equality.

1var nilS []int
2emptyS := []int{}
3madeS := make([]int, 0, 5)
4
5fmt.Println(nilS == nil)     // true
6fmt.Println(emptyS == nil)   // false
7fmt.Println(madeS == nil)    // false

JSON:

1n, _ := json.Marshal(nilS)   // "null"
2e, _ := json.Marshal(emptyS) // "[]"

When to use:

• Nil — uninitialized default.
• Empty — API responses requiring [].

Common mistakes:

• Returning nil from APIs.
• Checking only len == 0.
• append(nilSlice, ...) is safe.
• slices.Equal(nilS, emptyS) returns false.