Go: What is the difference between make and new?

make(T, args) — initializes slices, maps, and channels, returning a ready-to-use value. new(T) — allocates zeroed storage for any type, returning a *T pointer.

For slices, make accepts length and optional capacity arguments, allocating the backing array. For maps and channels, it initializes internal hash tables or ring buffers.

1s := make([]int, 5)       // [0 0 0 0 0], len=5, cap=5
2s2 := make([]int, 0, 100) // [], len=0, cap=100
3m := make(map[string]int) // ready to use
4ch := make(chan int, 1)   // buffered channel

new allocates memory and fills it with the zero value of T. It does NOT call any constructor — the returned pointer points to a zeroed value. For slices/maps/channels, the zero value is nil.

1p := new(int)    // *int → 0
2*p = 42
3
4q := new([]int)  // *[]int → nil
5*q = make([]int, 0, 10)  // still need make

When to use:

• make — always for slices, maps, channels.
• new — rarely; use &T{...} literal syntax instead for structs.

Common mistakes:

• Calling new([]int) and assuming the result is usable — it is a nil slice.
• Confusing make([]int, 10) (fills with zeros, len=10) with make([]int, 0, 10).
• Using make for non-slice/map/channel types — compilation error.
• Not preallocating with capacity hint — causes repeated reallocation.