Go: What is the difference between make and new?

make(T, ...) — initializes slices, maps, channels with usable state. new(T) — allocates zeroed memory, returns *T.

For slices, make([]int, 0, 100) preallocates backing storage. For maps/channels, make creates internal structures. The result is ready to use.

1s := make([]int, 0, 100)  // preallocated
2m := make(map[string]int) // ready to write
3ch := make(chan int, 10)  // buffered

new allocates sizeof(T) bytes, zeroes them, returns *T. For slices/maps/channels the zero value is nil — needs make to become usable.

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

When to use:

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

Common mistakes:

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