Why would I make() or new()?

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The introduction documents dedicate many paragraphs to explaining the difference between new() and make(), but in practice, you can create objects

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北海茫月

2020-11-29 15:34
- new(T) - Allocates memory, and sets it to the zero value for type T..
  ..that is 0 for int, "" for string and nil for referenced types (slice, map, chan)
  
  Note that referenced types are just pointers to some underlying data structures, which won't be created by new(T)
  Example: in case of slice, the underlying array won't be created, thus new([]int) returns a pointer to nothing
- make(T) - Allocates memory for referenced data types (slice, map, chan), plus initializes their underlying data structures
  
  Example: in case of slice, the underlying array will be created with the specified length and capacity
  Bear in mind that, unlike C, an array is a primitive type in Go!
That being said:
make(T) behaves like composite-literal syntax

new(T) behaves like var (when the variable is not initialized)

func main() {
    fmt.Println("-- MAKE --")
    a := make([]int, 0)
    aPtr := &a
    fmt.Println("pointer == nil :", *aPtr == nil)
    fmt.Printf("pointer value: %p\n\n", *aPtr)

    fmt.Println("-- COMPOSITE LITERAL --")
    b := []int{}
    bPtr := &b
    fmt.Println("pointer == nil :", *bPtr == nil)
    fmt.Printf("pointer value: %p\n\n", *bPtr)

    fmt.Println("-- NEW --")
    cPtr := new([]int)
    fmt.Println("pointer == nil :", *cPtr == nil)
    fmt.Printf("pointer value: %p\n\n", *cPtr)

    fmt.Println("-- VAR (not initialized) --")
    var d []int
    dPtr := &d
    fmt.Println("pointer == nil :", *dPtr == nil)
    fmt.Printf("pointer value: %p\n", *dPtr)
}

Run the program

-- MAKE --
pointer == nil : false
pointer value: 0x118eff0  # address to underlying array

-- COMPOSITE LITERAL --
pointer == nil : false
pointer value: 0x118eff0  # address to underlying array

-- NEW --
pointer == nil : true
pointer value: 0x0

-- VAR (not initialized) --
pointer == nil : true
pointer value: 0x0

Further reading:
https://golang.org/doc/effective_go.html#allocation_new https://golang.org/doc/effective_go.html#allocation_make

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