Go: What is the difference between make and new?

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

For slices, make([]int, 0, 500) creates a slice with preallocated backing storage. For maps, it creates the hash table. For channels, it allocates the ring buffer. The result is always immediately usable.

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

new allocates sizeof(T) bytes, zeroes them, and returns *T. For simple types this works fine. For slices/maps/channels, the zero value is nil — you must still call make to make them functional.

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, and channels.
• new — rarely in practice; prefer &T{...} literal syntax for struct initialization.

Common mistakes:

• Using new([]int) and trying to append — nil slice panic.
• Confusing make([]int, 10) (len=10, full of zeros) with make([]int, 0, 10) (len=0, cap=10).
• Not using the capacity hint — make([]int, 0, expectedSize) avoids repeated reallocation.
• Calling make on a non-slice/map/channel type — compilation error.