Go: What is the difference between make and new?

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

For slices, make([]int, 0, 100) creates a slice with preallocated capacity. For maps, it creates the hash table. For channels, it allocates the ring buffer. The result is always ready to use.

1buf := make([]byte, 0, 4096)  // preallocated buffer
2users := make(map[string]*User, 1000)  // capacity hint
3jobs := make(chan Job, 10)  // buffered channel

new returns a pointer to a zeroed value. For simple types this is fine, but for slices/maps/channels the zero value is nil — they need make before use.

1flag := new(bool)   // *bool → false, usable
2s := new([]int)     // *[]int → nil, NOT usable
3*s = make([]int, 0) // must call make

When to use:

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

Common mistakes:

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