一、一般操作
1,聲明變量，go自動(dòng)初始化為nil，長(zhǎng)度：0，地址：0，nil
func main(){
var ss []string;
fmt.Printf("length:%v \taddr:%p \tisnil:%v",len(ss),ss, ss==nil)
}
---
Running...
length:0 addr:0x0 isnil:true
Success: process exited with code 0.
2,切片的追加，刪除，插入操作
func main(){
var ss []string;
fmt.Printf("[ local print ]\t:\t length:%v\taddr:%p\tisnil:%v\n",len(ss),ss, ss==nil)
print("func print",ss)
//切片尾部追加元素append elemnt
for i:=0;i<10;i++{
ss=append(ss,fmt.Sprintf("s%d",i));
}
fmt.Printf("[ local print ]\t:\tlength:%v\taddr:%p\tisnil:%v\n",len(ss),ss, ss==nil)
print("after append",ss)
//刪除切片元素remove element at index
index:=5;
ss=append(ss[:index],ss[index+1:]...)
print("after delete",ss)
//在切片中間插入元素insert element at index;
//注意：保存后部剩余元素，必須新建一個(gè)臨時(shí)切片
rear:=append([]string{},ss[index:]...)
ss=append(ss[0:index],"inserted")
ss=append(ss,rear...)
print("after insert",ss)
}
func print(msg string,ss []string){
fmt.Printf("[ %20s ]\t:\tlength:%v\taddr:%p\tisnil:%v\tcontent:%v",msg,len(ss),ss, ss==nil,ss)
fmt.Println()
}
------
Running...
[ local print ] : length:0 addr:0x0 isnil:true
[ func print ] : length:0 addr:0x0 isnil:true content:[]
[ local print ] : length:10 addr:0xc208056000 isnil:false
[ after append ] : length:10 addr:0xc208056000 isnil:false content:[s0 s1 s2 s3 s4 s5 s6 s7 s8 s9]
[ after delete ] : length:9 addr:0xc208056000 isnil:false content:[s0 s1 s2 s3 s4 s6 s7 s8 s9]
[ after insert ] : length:10 addr:0xc208056000 isnil:false content:[s0 s1 s2 s3 s4 inserted s6 s7 s8 s9]
Success: process exited with code 0.
3，copy的使用。
在使用copy復(fù)制切片之前，要保證目標(biāo)切片有足夠的大小，注意是大小，而不是容量，還是看例子：
func main() {
var sa = make ([]string,0);
for i:=0;i<10;i++{
sa=append(sa,fmt.Sprintf("%v",i))
}
var da =make([]string,0,10);
var cc=0;
cc= copy(da,sa);
fmt.Printf("copy to da(len=%d)\t%v\n",len(da),da)
da = make([]string,5)
cc=copy(da,sa);
fmt.Printf("copy to da(len=%d)\tcopied=%d\t%v\n",len(da),cc,da)
da = make([]string,10)
cc =copy(da,sa);
fmt.Printf("copy to da(len=%d)\tcopied=%d\t%v\n",len(da),cc,da)
}
---
Running...
copy to da(len=0) []
copy to da(len=5) copied=5 [0 1 2 3 4]
copy to da(len=10) copied=10 [0 1 2 3 4 5 6 7 8 9]
從上面運(yùn)行結(jié)果，明顯看出，目標(biāo)切片大小0，容量10，copy不能復(fù)制。目標(biāo)切片大小小于源切片大小，copy就按照目標(biāo)切片大小復(fù)制，不會(huì)報(bào)錯(cuò)。
二、初始大小和容量
當(dāng)我們使用make初始化切片的時(shí)候，必須給出size。go語言的書上一般都會(huì)告訴我們，當(dāng)切片有足夠大小的時(shí)候，append操作是非常快的。但是當(dāng)給出初始大小后，我們得到的實(shí)際上是一個(gè)含有這個(gè)size數(shù)量切片類型的空元素，看例子：
func main(){
var ss=make([]string,10);
ss=append(ss,"last");
print("after append",ss)
}
---
Running...
[ after append ] : length:11 addr:0xc20804c000 isnil:false content:[ last]
實(shí)際上，此時(shí)我們應(yīng)該先用下標(biāo)為切片元素負(fù)值。但是如果我們既想有好的效率，有想繼續(xù)使用append函數(shù)而不想?yún)^(qū)分是否有空的元素，此時(shí)就要請(qǐng)出make的第三個(gè)參數(shù)，容量，也就是我們通過傳遞給make，0的大小和足夠大的容量數(shù)值就行了。
func main(){
var ss=make([]string,0,10);
ss=append(ss,"last");
print("after append",ss)
}
---
Running...
[ after append ] : length:1 addr:0xc20804a000 isnil:false content:[last]
三、切片的指針。
1，當(dāng)我們用append追加元素到切片時(shí)，如果容量不夠，go就會(huì)創(chuàng)建一個(gè)新的切片變量，看下面程序的執(zhí)行結(jié)果：
func main() {
var sa []string
fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);
for i:=0;i<10;i++{
sa=append(sa,fmt.Sprintf("%v",i))
fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);
}
fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);
}
---
Running ...
addr:0x0 len:0 content:[]
addr:0x1030e0c8 len:1 content:[0]
addr:0x10328120 len:2 content:[0 1]
addr:0x10322180 len:3 content:[0 1 2]
addr:0x10322180 len:4 content:[0 1 2 3]
addr:0x10342080 len:5 content:[0 1 2 3 4]
addr:0x10342080 len:6 content:[0 1 2 3 4 5]
addr:0x10342080 len:7 content:[0 1 2 3 4 5 6]
addr:0x10342080 len:8 content:[0 1 2 3 4 5 6 7]
addr:0x10324a00 len:9 content:[0 1 2 3 4 5 6 7 8]
addr:0x10324a00 len:10 content:[0 1 2 3 4 5 6 7 8 9]
addr:0x10324a00 len:10 content:[0 1 2 3 4 5 6 7 8 9]
//很明顯，切片的地址經(jīng)過了數(shù)次改變。
2,如果，在make初始化切片的時(shí)候給出了足夠的容量，append操作不會(huì)創(chuàng)建新的切片：
func main() {
var sa = make ([]string,0,10);
fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);
for i:=0;i<10;i++{
sa=append(sa,fmt.Sprintf("%v",i))
fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);
}
fmt.Printf("addr:%p \t\tlen:%v content:%v\n",sa,len(sa),sa);
}
addr:0x10304140 len:0 content:[]
addr:0x10304140 len:1 content:[0]
addr:0x10304140 len:2 content:[0 1]
addr:0x10304140 len:3 content:[0 1 2]
addr:0x10304140 len:4 content:[0 1 2 3]
addr:0x10304140 len:5 content:[0 1 2 3 4]
addr:0x10304140 len:6 content:[0 1 2 3 4 5]
addr:0x10304140 len:7 content:[0 1 2 3 4 5 6]
addr:0x10304140 len:8 content:[0 1 2 3 4 5 6 7]
addr:0x10304140 len:9 content:[0 1 2 3 4 5 6 7 8]
addr:0x10304140 len:10 content:[0 1 2 3 4 5 6 7 8 9]
addr:0x10304140 len:10 content:[0 1 2 3 4 5 6 7 8 9]
//可見，切片的地址一直保持不變
3, 如果不能準(zhǔn)確預(yù)估切片的大小，又不想改變變量（如：為了共享數(shù)據(jù)的改變），這時(shí)候就要請(qǐng)出指針來幫忙了，下面程序中，sa就是osa這個(gè)切片的指針，我們共享切片數(shù)據(jù)和操作切片的時(shí)候都使用這個(gè)切片地址就ok了，其本質(zhì)上是：append操作亦然會(huì)在需要的時(shí)候構(gòu)造新的切片，不過是將地址都保存到了sa中，因此我們通過該指針始終可以訪問到真正的數(shù)據(jù)。
func main() {
var osa = make ([]string,0);
sa:=&osa;
for i:=0;i<10;i++{
*sa=append(*sa,fmt.Sprintf("%v",i))
fmt.Printf("addr of osa:%p,\taddr:%p \t content:%v\n",osa,sa,sa);
}
fmt.Printf("addr of osa:%p,\taddr:%p \t content:%v\n",osa,sa,sa);
}
---
Running...
addr of osa:0xc20800a220, addr:0xc20801e020 content:&[0]
addr of osa:0xc20801e0a0, addr:0xc20801e020 content:&[0 1]
addr of osa:0xc20803e0c0, addr:0xc20801e020 content:&[0 1 2]
addr of osa:0xc20803e0c0, addr:0xc20801e020 content:&[0 1 2 3]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4 5]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4 5 6]
addr of osa:0xc208050080, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7]
addr of osa:0xc208052000, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7 8]
addr of osa:0xc208052000, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7 8 9]
addr of osa:0xc208052000, addr:0xc20801e020 content:&[0 1 2 3 4 5 6 7 8 9]
package main
import (
"errors"
"fmt"
"reflect"
)
// 判斷obj是否在target中，target支持的類型arrary,slice,map
func Contain(obj interface{}, target interface{}) (bool, error) {
targetValue := reflect.ValueOf(target)
switch reflect.TypeOf(target).Kind() {
case reflect.Slice, reflect.Array:
for i := 0; i < targetValue.Len(); i++ {
if targetValue.Index(i).Interface() == obj {
return true, nil
}
}
case reflect.Map:
if targetValue.MapIndex(reflect.ValueOf(obj)).IsValid() {
return true, nil
}
}
return false, errors.New("not in array")
}
func main() {
testMap()
testArray()
testSlice()
}
func testArray() {
a := 1
b := [3]int{1, 2, 3}
fmt.Println(Contain(a, b))
c := "a"
d := [4]string{"b", "c", "d", "a"}
fmt.Println(Contain(c, d))
e := 1.1
f := [4]float64{1.2, 1.3, 1.1, 1.4}
fmt.Println(Contain(e, f))
g := 1
h := [4]interface{}{2, 4, 6, 1}
fmt.Println(Contain(g, h))
i := [4]int64{}
fmt.Println(Contain(a, i))
}
func testSlice() {
a := 1
b := []int{1, 2, 3}
fmt.Println(Contain(a, b))
c := "a"
d := []string{"b", "c", "d", "a"}
fmt.Println(Contain(c, d))
e := 1.1
f := []float64{1.2, 1.3, 1.1, 1.4}
fmt.Println(Contain(e, f))
g := 1
h := []interface{}{2, 4, 6, 1}
fmt.Println(Contain(g, h))
i := []int64{}
fmt.Println(Contain(a, i))
}
func testMap() {
var a = map[int]string{1: "1", 2: "2"}
fmt.Println(Contain(3, a))
var b = map[string]int{"1": 1, "2": 2}
fmt.Println(Contain("1", b))
var c = map[string][]int{"1": {1, 2}, "2": {2, 3}}
fmt.Println(Contain("6", c))
}