直接上代码

var group []string
    group[0]="abc"
    fmt.Println(group[0])

编译正常，运行报错如下

panic: runtime error: index out of range

goroutine 1 [running]:
panic(0x47a880, 0xc42000a110)
    /opt/tools/go1.7.3/src/runtime/panic.go:500 +0x1a1
main.main()
    /opt/IdeaProjects/test-embeded-struct/main.go:11 +0x14
exit status 2

index越界，于是改了一下代码

    var group []string
    fmt.Println(len(group))
    fmt.Println(cap(group))
    group[0]="abc"
    fmt.Println(group[0])

0
0
panic: runtime error: index out of range

goroutine 1 [running]:
panic(0x48fec0, 0xc42000a110)
    /opt/tools/go1.7.3/src/runtime/panic.go:500 +0x1a1
main.main()
    /opt/IdeaProjects/test-embeded-struct/main.go:13 +0x10a
exit status 2

也就是说，slice声明的时候如果不同时初始化数据，默认长度和容量都是0，下标0意味着长度是1，所以index越界了。

那么，使用slice的时候有下面几种方式

，
第一，声明的时候初始化数据，例如

test:=[]string{"a","b","c"}

第二，从已经初始化数据的slice‘切’出来

test:=[]string{"a","b","c"}
your_string=test[0:1]

第三，append方法，会默认扩容，

var group []string
fmt.Println(len(group))
fmt.Println(cap(group))
group=append(group,"hahaha")
group[0]="abc"
fmt.Println(len(group))
fmt.Println(cap(group))
fmt.Println(group[0])

0
0
1
1
abc

append方法在slice长度不足的时候，会进行扩容，注释如下

// The append built-in function appends elements to the end of a slice. If
// it has sufficient capacity, the destination is resliced to accommodate the
// new elements. If it does not, a new underlying array will be allocated.
// Append returns the updated slice. It is therefore necessary to store the
// result of append, often in the variable holding the slice itself:
//  slice = append(slice, elem1, elem2)
//  slice = append(slice, anotherSlice...)
// As a special case, it is legal to append a string to a byte slice, like this:
//  slice = append([]byte("hello "), "world"...)
func append(slice []Type, elems ...Type) []Type