Go: What is the difference between make and new?

make(T, ...) — creates 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, 5, 10) creates a slice with 5 zero-valued elements and capacity 10. For maps and channels, it allocates the necessary internal structures. The key point is that make produces a value ready for immediate use.

1s := make([]int, 0, 100)  // preallocated for 100 elements
2for i := 0; i < 100; i++ {
3    s = append(s, i)  // no reallocation
4}
5
6m := make(map[string]int, 10)  // hint for ~10 entries
7ch := make(chan int)            // unbuffered channel

new is more primitive. It returns a pointer to zeroed memory. For simple types this works, but for slices/maps/channels the zero value is nil — you must still call make to make them functional.

1p := new(int)     // *int → 0
2s := new([]int)   // *[]int → nil (unusable until make)
3*s = make([]int, 0, 10)

When to use:

• make — always for slices, maps, channels.
• new — rarely in practice; prefer &T{...} 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).
• Passing make results to functions that modify them — make returns a value, not a reference.