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聊聊Golang中的make和new
source link: https://www.tuicool.com/articles/AZbaMzF
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概述
根据 官方文档 描述
make是用来分配并且初始化slice,map,chan等类型的对象 new也是用来分配内存的,返回对应内向的0值的指针,但并不初始化对象
看下面例子,就很明显了
a := new([]int)
b := make([]int,1)
fmt.Println(a)
fmt.Println(b)
fmt.Println(unsafe.Sizeof(*a))
fmt.Println(unsafe.Sizeof(b)+unsafe.Sizeof([1]int{}))
output:
&[]
[0]
24
32
make
make在初始化不同类型对象时,会调用不同的函数.
make slice时会调用 runtime.makeslice
make map时会调用 runtime.makemap或者runtime.makemap_small
make chan 时会调用 runtime.makechan
b := make([]int,1) fmt.Println(b)
以slice为例,转成汇编后能看见如下代码
PCDATA $0, $0 CALL runtime.makeslice(SB) 这里 MOVQ 32(SP), AX MOVQ 24(SP), CX MOVQ 40(SP), DX
PCDATA $0, $0 CALL runtime.makemap_small(SB) MOVQ (SP), AX
new
以下面代码为例
a := new([]int) fmt.Println(a)
转成汇编语言后能看下如下代码:
PCDATA $0, $0 CALL runtime.newobject(SB) MOVQ 8(SP), AX XORPS X0, X0
可以看到最终会调用 runtime.newobject 来分配内存,并且返回指针
func newobject(typ *_type) unsafe.Pointer {
return mallocgc(typ.size, typ, true)
}
参考资料
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