Go: What is the difference between make and new?

make(T, ...) — allocates and initializes slices, maps, and channels, returning a usable (non-nil) value. new(T) — allocates zeroed memory for any type and returns a pointer to it.

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

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

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

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:

• Using new([]int) and calling append — nil slice panic.
• make([]int, 10) creates 10 zero elements, not an empty slice with cap 10.
• Not using the capacity hint causes repeated reallocation.
• Calling make on non-slice/map/channel — compile error.