break    default      func    interface    select
	case     defer        go      map          struct
	chan     else         goto    package      switch
	const    fallthrough  if      range        type
	continue for          import  return       var

func Arr() {

	arr := [3]int{1, 2, 3}
	arr0 := [...]int{1, 2, 3}

	fmt.Println(arr, arr0)
}

// 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 CapOfSlice() {
	s := []int{}

    // len:  0    cap:  0
	preCap := 0

	for i := 0; i < 1000; i++ {
		s = append(s, i)
		if cap(s) != preCap {
			fmt.Println("len: ", len(s), "   cap: ", cap(s))
			preCap = cap(s)
		}
	}
	// 	len:  1    cap:  1
	// len:  2    cap:  2
	// len:  3    cap:  4
	// len:  5    cap:  8
	// len:  9    cap:  16
	// len:  17    cap:  32
	// len:  33    cap:  64
	// len:  65    cap:  128
	// len:  129    cap:  256
	// len:  257    cap:  512
	// len:  513    cap:  1024
}

// growslice handles slice growth during append.
// It is passed the slice element type, the old slice, and the desired new minimum capacity,
// and it returns a new slice with at least that capacity, with the old data
// copied into it.
// The new slice's length is set to the old slice's length,
// NOT to the new requested capacity.
// This is for codegen convenience. The old slice's length is used immediately
// to calculate where to write new values during an append.
// TODO: When the old backend is gone, reconsider this decision.
// The SSA backend might prefer the new length or to return only ptr/cap and save stack space.
func growslice(et *_type, old slice, cap int) slice {
	if raceenabled {
		callerpc := getcallerpc()
		racereadrangepc(old.array, uintptr(old.len*int(et.size)), callerpc, funcPC(growslice))
	}
	if msanenabled {
		msanread(old.array, uintptr(old.len*int(et.size)))
	}

	if cap < old.cap {
		panic(errorString("growslice: cap out of range"))
	}

	if et.size == 0 {
		// append should not create a slice with nil pointer but non-zero len.
		// We assume that append doesn't need to preserve old.array in this case.
		return slice{unsafe.Pointer(&zerobase), old.len, cap}
	}

	newcap := old.cap
	doublecap := newcap + newcap
	if cap > doublecap {
		newcap = cap
	} else {
		if old.len < 1024 {
			newcap = doublecap
		} else {
			// Check 0 < newcap to detect overflow
			// and prevent an infinite loop.
			for 0 < newcap && newcap < cap {
				newcap += newcap / 4
			}
			// Set newcap to the requested cap when
			// the newcap calculation overflowed.
			if newcap <= 0 {
				newcap = cap
			}
		}
	}

	var overflow bool
	var lenmem, newlenmem, capmem uintptr
	// Specialize for common values of et.size.
	// For 1 we don't need any division/multiplication.
	// For sys.PtrSize, compiler will optimize division/multiplication into a shift by a constant.
	// For powers of 2, use a variable shift.
	switch {
	case et.size == 1:
		lenmem = uintptr(old.len)
		newlenmem = uintptr(cap)
		capmem = roundupsize(uintptr(newcap))
		overflow = uintptr(newcap) > maxAlloc
		newcap = int(capmem)
	case et.size == sys.PtrSize:
		lenmem = uintptr(old.len) * sys.PtrSize
		newlenmem = uintptr(cap) * sys.PtrSize
		capmem = roundupsize(uintptr(newcap) * sys.PtrSize)
		overflow = uintptr(newcap) > maxAlloc/sys.PtrSize
		newcap = int(capmem / sys.PtrSize)
	case isPowerOfTwo(et.size):
		var shift uintptr
		if sys.PtrSize == 8 {
			// Mask shift for better code generation.
			shift = uintptr(sys.Ctz64(uint64(et.size))) & 63
		} else {
			shift = uintptr(sys.Ctz32(uint32(et.size))) & 31
		}
		lenmem = uintptr(old.len) << shift
		newlenmem = uintptr(cap) << shift
		capmem = roundupsize(uintptr(newcap) << shift)
		overflow = uintptr(newcap) > (maxAlloc >> shift)
		newcap = int(capmem >> shift)
	default:
		lenmem = uintptr(old.len) * et.size
		newlenmem = uintptr(cap) * et.size
		capmem, overflow = math.MulUintptr(et.size, uintptr(newcap))
		capmem = roundupsize(capmem)
		newcap = int(capmem / et.size)
	}

	// The check of overflow in addition to capmem > maxAlloc is needed
	// to prevent an overflow which can be used to trigger a segfault
	// on 32bit architectures with this example program:
	//
	// type T [1<<27 + 1]int64
	//
	// var d T
	// var s []T
	//
	// func main() {
	//   s = append(s, d, d, d, d)
	//   print(len(s), "\n")
	// }
	if overflow || capmem > maxAlloc {
		panic(errorString("growslice: cap out of range"))
	}

	var p unsafe.Pointer
	if et.ptrdata == 0 {
		p = mallocgc(capmem, nil, false)
		// The append() that calls growslice is going to overwrite from old.len to cap (which will be the new length).
		// Only clear the part that will not be overwritten.
		memclrNoHeapPointers(add(p, newlenmem), capmem-newlenmem)
	} else {
		// Note: can't use rawmem (which avoids zeroing of memory), because then GC can scan uninitialized memory.
		p = mallocgc(capmem, et, true)
		if lenmem > 0 && writeBarrier.enabled {
			// Only shade the pointers in old.array since we know the destination slice p
			// only contains nil pointers because it has been cleared during alloc.
			bulkBarrierPreWriteSrcOnly(uintptr(p), uintptr(old.array), lenmem)
		}
	}
	memmove(p, old.array, lenmem)

	return slice{p, old.len, newcap}
}

// StringHeader is the runtime representation of a string.
// 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 StringHeader struct {
	Data uintptr
	Len  int
}

// stringHeader is a safe version of StringHeader used within this package.
type stringHeader struct {
	Data unsafe.Pointer
	Len  int
}

// The new built-in function allocates memory. The first argument is a type,
// not a value, and the value returned is a pointer to a newly
// allocated zero value of that type.
func new(Type) *Type

func RangeString() {

	s := "fhjfhjdf在"

	for i, val := range s {

		fmt.Println(i, val)
	}
    fmt.Println(len(s))

}
//output 

0 102
1 104
2 106
3 102
4 104
5 106
6 100
7 102
8 22312
11

func DeferFunc1(i int) (t int) {
	t = i
	defer func() {
		t += 3
		fmt.Println("t in defer1: ", t)
	}()
	return t

	// t in defer1:  4
	// t in func result: 4
}

func DeferFunc2(i int) int {
	t := i
	defer func() {
		t += 3
		fmt.Println("t in defer2: ", t)
	}()
	return t
}

	// t in defer2:  4
	// t in func result: 1

func VarInDefer1() {

	var i = 1
	defer fmt.Println("result: ", func() int { return i * 2 }())
	i++
}
// output
result:  2


// 向 defer 关键字传入匿名函数
func VarInDefer() {

	var i = 1
	defer func() {
		fmt.Println("result: ", func() int { return i * 2 }())
	}()
	i++
}

// output
result:  4

func VarInDefer() {

	startedAt := time.Now()
	defer func() { fmt.Println("defer time: ", time.Since(startedAt)) }()

	time.Sleep(time.Second)

	fmt.Println("return time: ", time.Since(startedAt))

	// 	return time:  1.003767335s
	// defer time:  1.003916954s
}

func VarInDefer1() {

	startedAt := time.Now()
	defer fmt.Println("defer time: ", time.Since(startedAt))

	time.Sleep(time.Second)
	fmt.Println("return time: ", time.Since(startedAt))
	
	// 	return time:  1.002410955s
	// defer time:  205ns
}

func DeferPanicTest() {
	defer recover()

	panic("test panic")
}
// panic

func DeferPanicTest1() {
	defer func() {
		fmt.Println("recover......")
		recover()
	}()
	panic("test panic")
}
// recover......