make function allocates and initializes an object of type slice, map, or chan only. Like new, the first argument is a type. But, it can also take a second argument, the size. Unlike new, make’s return type is the same as the type of its argument, not a pointer to it. And the allocated value is initialized (not set to zero value like in new). The reason is that slice, map and chan are data structures. They need to be initialized, otherwise they won't be usable. This is the reason new() and make() need to be different.

下面是Effective Go的例子:

p *[]int = new([]int) // *p = nil, which makes p useless
v []int = make([]int, 100) // creates v structure that has pointer to an array, length field, and capacity field. So, v is immediately usable

new()和make()的区别:

new(T)为一个类型为T的新项分配零存储，并返回它的地址，一个类型为*T的值:它返回一个指向新分配的类型为T的零值的指针，准备使用;它适用于数组和结构等值类型;它是 等价于&T{} make(T)返回一个初始化的T类型值;它只适用于3种内置的引用类型:切片、映射和通道。

换句话说，新的分配;使初始化;

var p *[]int = new([]int)
or
// *p == nil; with len and cap 0
p := new([]int)

这很少有用。

p := make([]int, 0)

我们的切片已经初始化，但这里指向一个空数组。

这两种说法都不是很有用，下面是:

var v []int = make([]int, 10, 50)
// Or
v := make([]int, 10, 50)

这将分配一个50个整型数组，然后创建一个长度为10，容量为50的切片v，指向数组的前10个元素。

找出make()和new()的一些规则:

对于切片、映射和通道:使用make 对于数组、结构和所有值类型:使用new

package main
type Foo map[string]string
type Bar struct {
         s string
         i int
}
func main() {
         // OK:
         y := new(Bar)
         (*y).s = "hello"
         (*y).i = 1

         // NOT OK:
         z := make(Bar) // compile error: cannot make type Bar
         z.s = "hello"
         z.i = 1

         // OK:
         x := make(Foo)
         x["x"] = "goodbye"
         x["y"] = "world"

         // NOT OK:
         u := new(Foo)
         (*u)["x"] = "goodbye" // !!panic!!: runtime error: 
                   // assignment to entry in nil map
         (*u)["y"] = "world"
}

渠道:

func main() {
    // OK:
    ch := make(chan string)
    go sendData(ch)
    go getData(ch)
    time.Sleep(1e9)

    // NOT OK:
    ch := new(chan string)
    go sendData(ch) // cannot use ch (variable of type *chan string) 
                   // as chan string value in argument to sendData
    go getData(ch)
    time.Sleep(1e9)
}

func sendData(ch chan string) {
    ch <- "Washington"
    ch <- "Tripoli"
    ch <- "London"
    ch <- "Beijing"
    ch <- "Tokio"
}

func getData(ch chan string) {
    var input string
    for {
        input = <-ch
        fmt.Printf("%s ", input)

    }
}

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!

话虽如此: make(T)的行为类似于复合文字语法 new(T)的行为类似于var(当变量未初始化时)

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)
}

运行程序

-- 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

进一步阅读: https://golang.org/doc/effective_go.html#allocation_new https://golang.org/doc/effective_go.html#allocation_make

“make”的好处在其他答案中有很多，但是“New”比上面没有提到的make有一个额外的好处:泛型(截至1.18)。

假设你有一组平面(所有字段都是原语)结构体，如下所示:

type SomeStruct struct {
    V1 string `json:"v1"`
    V2 string `json:"v2"`
}

你想要创建一个映射函数，将一个map[string]字符串转换为任何结构体。然后你可以这样写:

func GetStructFromMap[T any](values map[string]string) (T, error) {
    myStr := T{}
    bytes, err := json.Marshal(values)
    if err != nil {
        return *myStr, err
    }

    if err := json.Unmarshal(bytes, str); err != nil {
        return *myStr, err
    }

    return *myStr, nil
}

但是，这段代码将抛出一个关于myStr:= T{}行的错误，关于无效的组合值。用myStr:= make(T)替换它会产生另一个关于没有底层类型的错误。因此，您需要将该行替换为myStr:= new(T)，这将创建一个对该结构的零值实例的引用。

可以看到，在处理泛型时，new可以用来实例化编译时未知的类型。

另一方面，在这个特定的示例中还可以使用命名返回类型，但更普遍的用法仍然有效。

new(T):它返回一个指向类型T的指针，一个类型为*T的值，它分配并归零内存。new(T)等价于&T{}。

make(T):返回类型为T的初始化值，分配并初始化内存。它用于切片，映射和通道。

已经有很多很好的答案，但是让我解释一下new()和make()作为单独的分配器的必要性。

new(T)分配给定类型T的未初始化的零内存，并返回指向该内存的指针，以便它可以使用。归零仅仅意味着分配的内存中给定类型的值为零。某些go类型的零值为- Int - 0 Bool - false Float - 0 字符串- "" struct -每个成员的零值

Problem with new() arises when it needs to handle three other composite types - chan, slice and map. These three types are special in essence that their underlying type is not just an another type but rather a state that needs to be initialized. For example , the underlying state of a slice consists of a pointer to the first element of internal array storage, a length that determines number of elements that can be accessed and a capacity that increases as the number of elements grow. new() certainly cannot handle allocation of such types due to their need for extra initialization step, that is where make() come into play.

make(T, args)是专门为chan, slice和map类型创建的。它不仅分配chan、slice和map的内部存储类型，而且还初始化它们的底层状态，使它们可以使用。例如，对于片，它分配内部数组存储，设置指针指向该数组中的第一个元素，并设置长度和容量值。