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

Nil slice — zero value, no backing array, pointer/length/capacity all zero. Empty slice — has backing array but no elements; len == 0.

Both support the same operations identically. The key differences are in identity checks and JSON serialization.

1var nilS []int        // nil
2emptyS := []int{}     // non-nil, empty
3madeS := make([]int, 0, 10)  // non-nil, empty, cap=10
4
5fmt.Println(nilS == nil)     // true
6fmt.Println(emptyS == nil)   // false
7fmt.Println(madeS == nil)    // false

JSON behavior:

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

When to use:

• Nil — default uninitialized state; no memory.
• Empty — API responses requiring [] not null.

Common mistakes:

• Returning nil from APIs — null vs [] mismatch.
• Checking only len == 0 when nil vs empty matters.
• append(nilSlice, ...) is safe.
• slices.Equal(nilS, emptyS) returns false.