Go: What is the difference between make and new?

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

For slices, make([]int, 0, 500) preallocates backing storage for 500 elements. For maps and channels, make sets up hash tables and ring buffers. The result is always immediately usable.

1s := make([]int, 0, 500)   // preallocated
2m := make(map[string]int)  // ready to write
3ch := make(chan int, 10)   // buffered channel

new allocates sizeof(T) bytes, zeroes them, returns *T. For simple types this works fine. For slices/maps/channels, the zero value is nil — unusable until make is called.

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

When to use:

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

Common mistakes:

• new([]int) returns nil slice — must make to use.
• make([]int, 10) has len=10 (zeros), not empty with cap=10.
• Not using capacity hint — causes repeated allocations.
• make on non-slice/map/channel — compile error.