slice创建slice 下标通过下标的方式获得数组或者切片的一部分；使用下标初始化切片不会拷贝原数组或者原切片中的

len and cpacity

The length of a slice is the number of elements it contains.

The capacity of a slice is the number of elements in the underlying array, counting from the first element in the slice.

SliceHeader

gosamples.dev/capacity-an…

/src/reflect/value.go

// SliceHeader is the runtime representation of a slice.
// It cannot be used safely or portably and its representation may
// change in a later release.
// Moreover, the Data field is not sufficient to guarantee the data
// it references will not be garbage collected, so programs must keep
// a separate, correctly typed pointer to the underlying data.
type SliceHeader struct {
   Data uintptr
   Len  int
   Cap  int
}

func Append(s Value, x ...Value) Value {
   s.mustBe(Slice)
   s, i0, i1 := grow(s, len(x))
   for i, j := i0, 0; i < i1; i, j = i+1, j+1 {
      s.Index(i).Set(x[j])
   }
   return s
}

func grow(s Value, extra int) (Value, int, int) {
   i0 := s.Len()
   i1 := i0 + extra
   if i1 < i0 {
      panic("reflect.Append: slice overflow")
   }
   m := s.Cap()
   if i1 <= m {
      return s.Slice(0, i1), i0, i1
   }
   if m == 0 {
      m = extra
   } else {
      const threshold = 256
      for m < i1 {
         if i0 < threshold {
            m += m
         } else {
            m += (m + 3*threshold) / 4
         }
      }
   }
   t := MakeSlice(s.Type(), i1, m)
   Copy(t, s)
   return t, i0, i1
}

创建slice

下标

通过下标的方式获得数组或者切片的一部分；

使用下标初始化切片不会拷贝原数组或者原切片中的数据，它只会创建一个指向原数组的切片结构体，所以修改新切片的数据也会修改原切片。

字面量

s :=[] int {1,2,3 }

make

使用关键字 make 创建切片：make([]T, length, capacity)

(len 是数组的长度并且也是切片的初始长度, capacity 为容量，len指向的单元格会初始化为0值）

为什么需要capacity?因为扩容会触发拷贝，指定capacity能一定程度上避免扩容，提升性能

var 声明后赋值

var slice1 []int 
slice1[0] = 1

创建定长数组

balance := [5]float32{1000.0, 2.0, 3.4, 7.0, 50.0}

var balance [5]float32
balance[0] = 1000.0

slice