Go: What is the difference between make and new?

make(T, ...) — allocates and initializes slices, maps, and channels. new(T) — allocates zeroed storage for any type, returns a pointer.

For slices, make sets up the backing array with the specified length and capacity. For maps, it creates the hash table. For channels, it allocates the send/receive buffer.

1s := make([]int, 0, 1000)  // preallocate for 1000 items
2m := make(map[string]int, 100)  // hint for ~100 entries
3ch := make(chan int, 50)   // buffered channel

new allocates sizeof(T) bytes, zeroes them, returns *T. For simple types (int, bool) this is fine. For slices/maps/channels, the zero value is nil — unusable without make.

1p := new(int)    // *int → 0, usable
2s := new([]int)  // *[]int → nil, NOT usable
3// Must: *s = make([]int, 0)

When to use:

• make — always for slices, maps, channels.
• new — rarely; prefer &T{...} for structs.

Common mistakes:

• new([]int) → nil slice, needs make.
• make([]int, 10) → len=10 (zeros), not empty with cap=10.
• Not using capacity hint — causes reallocation.
• make on non-slice/map/channel — compile error.