Go的函数参数总是传值

依照Go的 FQA , 函数的参数传递总是传值的(pass-by-value): As in all languages in the C family, everythi

依照Go的 FQA

, 函数的参数传递总是传值的(pass-by-value):

As in all languages in the C family, everything in Go is passed by value. That is, a function always gets a copy of the thing being passed, as if there were an assignment statement assigning the value to the parameter. For instance, passing an int value to a function makes a copy of the int, and passing a pointer value makes a copy of the pointer, but not the data it points to. (See a later section

for a discussion of how this affects method receivers.)

Map and slice values behave like pointers: they are descriptors that contain pointers to the underlying map or slice data. Copying a map or slice value doesn't copy the data it points to. Copying an interface value makes a copy of the thing stored in the interface value. If the interface value holds a struct, copying the interface value makes a copy of the struct. If the interface value holds a pointer, copying the interface value makes a copy of the pointer, but again not the data it points to.

以下是测试代码,结果贴在下面,不解释了。

packagemain

import(

"fmt"

"reflect"

"unsafe"

)

funcprintInt(iint) {

fmt.Printf("int i: %p/n", &i)

}

funcprintInt2(i *int) {

fmt.Printf("int i: %p/n", i)

}

funcprintStr(sstring) {

fmt.Printf("string s: %p/n", &s)

hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))

data := hdr.Data

fmt.Printf("string s data: 0x%x/n", data)

}

funcprintStr2(s *string) {

fmt.Printf("string s: %p/n", s)

hdr := (*reflect.StringHeader)(unsafe.Pointer(s))

data := hdr.Data

fmt.Printf("string s data: 0x%x/n", data)

}

funcprintSlice(s []int) {

fmt.Printf("slice s: %p/n", &s)

hdr := (*reflect.SliceHeader)(unsafe.Pointer(&s))

data := hdr.Data

fmt.Printf("slice s data: 0x%x/n", data)

}

funcprintSlice2(s *[]int) {

fmt.Printf("slice s: %p/n", s)

hdr := (*reflect.SliceHeader)(unsafe.Pointer(s))

data := hdr.Data

fmt.Printf("slice s data: 0x%x/n", data)

}

typeSstruct{

I int

}

funcprintStruct(s S) {

fmt.Printf("struct s: %p, I: %p/n", &s, &(s.I))

}

funcprintStruct2(s *S) {

fmt.Printf("struct s: %p, I: %p/n", &s, &(s.I))

}

funcprintInterface(iinterface{}) {

fmt.Printf("int i: %p/n", &i)

}

funcprintInterface2(iinterface{}) {

s := i.(S)

fmt.Printf("struct s: %p, I: %p/n", &s, &(s.I))

}

funcprintInterface3(iinterface{}) {

s := i.(*S)

fmt.Printf("struct s: %p, I: %p/n", s, &(s.I))

}

funcmain() {

//test int

i :=10

fmt.Printf("int i: %p/n", &i)

printInt(i)

printInt2(&i)

//test string

s := "hello, world"

fmt.Printf("/n/nstring s: %p/n", &s)

hdr := (*reflect.StringHeader)(unsafe.Pointer(&s))

data := hdr.Data

fmt.Printf("string s data: 0x%x/n", data)

printStr(s)

printStr2(&s)

//slice and map

sl := []int{1,2,3,4,5}

fmt.Printf("/n/nslice s: %p/n", &sl)

hdr2 := (*reflect.SliceHeader)(unsafe.Pointer(&sl))

data = hdr2.Data

fmt.Printf("slice s data: 0x%x/n", data)

printSlice(sl)

printSlice2(&sl)

//struct

ss := S{I:10}

ssp := &ss

fmt.Printf("/n/nstruct s: %p, I: %p/n", ssp, &(ss.I))

printStruct(ss)

printStruct2(ssp)

//interface to int

fmt.Printf("/n/nint i: %p/n", &i)

printInterface(i)

//interface to struct

fmt.Printf("/n/nstruct s: %p, I: %p/n", ssp, &(ss.I))

printInterface2(ss)

printInterface3(ssp)

}

输出结果:

inti:0xc420074188

inti:0xc4200741b8

inti:0xc420074188

string s: 0xc4200741c0

string s data: 0xa778d

string s: 0xc4200741e0

string s data: 0xa778d

string s: 0xc4200741c0

string s data: 0xa778d

slice s: 0xc42006e0c0

slice s data: 0xc4200780c0

slice s: 0xc42006e0e0

slice s data: 0xc4200780c0

slice s: 0xc42006e0c0

slice s data: 0xc4200780c0

struct s: 0xc420074210, I:0xc420074210

struct s: 0xc420074218, I:0xc420074218

struct s: 0xc420084020, I:0xc420074210

inti:0xc420074188

inti:0xc420074230

struct s: 0xc420074210, I:0xc420074210

struct s: 0xc420074228, I:0xc420074228

struct s: 0xc420074210, I:0xc420074210

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