Golang 中 new 和 make的區別

Golang 內置兩個函數，new 和 make ,其做用都是用來分配內存的。這麼說可能會形成混淆，但其實規則很簡單，其實他們適用於不一樣的類型。

• make 函數只用於給 slice、map、channel進行初始化；
• new 函數參數爲 一個類型不是一個值，用該類型的零值初始化一塊空間，並返回該空間的指針。

咱們看一下下面的案例：

package main

import (
	"fmt"
)

func main() {
	var i *int

	*i=10
	fmt.Println(*i)

}
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運行報錯，panic: runtime error: invalid memory address or nil pointer dereference。錯誤很明顯提示無效的內存地址或者空指針錯誤。
如何解決呢，很簡單，咱們只須要使用new來進行內存分配。

package main

import (
	"fmt"
)

func main() {
	var i *int
	i = new(int)
	*i = 10
	fmt.Println(*i)

}
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再次運行，完美輸出結果 10 。
咱們再經過源碼看看new 函數

// The new built-in function allocates memory. The first argument is a type,
// not a value, and the value returned is a pointer to a newly
// allocated zero value of that type.
func new(Type) *Type
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只接收一個參數（type），而且返回了一個初始化爲零值的內存指針。

再看看 make 函數

// The make built-in function allocates and initializes an object of type
// slice, map, or chan (only). Like new, the first argument is a type, not a
// value. Unlike new, make's return type is the same as the type of its // argument, not a pointer to it. The specification of the result depends on // the type: // Slice: The size specifies the length. The capacity of the slice is // equal to its length. A second integer argument may be provided to // specify a different capacity; it must be no smaller than the // length. For example, make([]int, 0, 10) allocates an underlying array // of size 10 and returns a slice of length 0 and capacity 10 that is // backed by this underlying array. // Map: An empty map is allocated with enough space to hold the // specified number of elements. The size may be omitted, in which case // a small starting size is allocated. // Channel: The channel's buffer is initialized with the specified
//	buffer capacity. If zero, or the size is omitted, the channel is
//	unbuffered.
func make(t Type, size ...IntegerType) Type
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• 只爲 slice, map, or chan (only)分配內存和初始化；
• 和 new 函數同樣的是第一個參數是一個 type 不是 value；
• 和 new 函數不一樣的是make 返回的不是指針，返回的是參數中傳遞進來的類型自己；

你確定會困惑，爲何make 不返回指針呢，由於slice, map, or chan自己就是引用類型。具體能夠查看文章深刻理解 Slice

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