Go: What is the difference between make and new?

make — creates and initializes slices, maps, and channels with usable internal state. new — allocates zeroed memory for any type and returns a pointer.

For slices, make sets up the backing array and internal header (pointer, length, capacity). For maps, it creates the hash table. For channels, it allocates the send/receive buffer. The result is always a ready-to-use value.

1s := make([]int, 0, 1000)  // preallocate for 1000 items
2m := make(map[string]bool) // empty but usable
3ch := make(chan int, 50)    // buffered channel

new is simpler: it allocates sizeof(T) bytes, zeroes them, and returns *T. For value types (int, bool, small structs) this works. For slices/maps/channels, the zero value is nil, which panics on use until make is called.

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

When to use:

• make — always for slices, maps, and channels.
• new — rarely; prefer &T{field: value} 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: make([]int, 0, expectedSize) avoids repeated reallocation.
• Calling make on a non-slice/map/channel — compile error.