//在栈中的slice
type slice struct {
	array unsafe.Pointer
	len   int
	cap   int
}

//在堆中的slice
type notInHeapSlice struct {
	array *notInHeap
	len   int
	cap   int
}

package main

import "fmt"

func main() {
	memoryCap()
}

func memoryCap() {
	s := []int{}

	for i := 0; i < 16; i++ {
		fmt.Printf("分配内存的大小：%d \n", cap(s))
		fmt.Println(s)
		s = append(s, i)
	}
}

func makeslice(et *_type, len, cap int) unsafe.Pointer {
	mem, overflow := math.MulUintptr(et.size, uintptr(cap))
	if overflow || mem > maxAlloc || len < 0 || len > cap {
		// 简单来说，makeslice函数的工作主要就是计算slice所需内存大小，然后调用mallocgc进行内存的分配。计算slice所需内存又是通过MulUintptr来实现的，MulUintptr的源码我也已经贴出，主要就是用切片中元素大小和切片的容量相乘计算出所需占用的内存空间，如果内存溢出，或者计算出的内存大小大于最大可分配内存，MulUintptr的overflow会返回true，makeslice就会报错。另外如果传入长度小于0或者长度小于容量，makeslice也会报错
		// 可以查看这个issue golang.org/issue/4085.
		mem, overflow := math.MulUintptr(et.size, uintptr(len))
		if overflow || mem > maxAlloc || len < 0 {
			panicmakeslicelen()
		}
		panicmakeslicecap()
	}

	return mallocgc(mem, et, true)
}

// 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 {
    ...

    //这边未扩容逻辑
	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-et.size+et.ptrdata)
		}
	}
	memmove(p, old.array, lenmem)

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

package main

import "fmt"

func main() {
	s := []int{-1, -1}
	fmt.Println(s)
	sliceChange(s)
	fmt.Println(s)
}

func sliceChange(s []int) {
	s[0] = 1
	s[1] = 1
	s = append(s, 2)
	fmt.Println("change:", s)
}

package main

import "fmt"

func main() {
	s2 := make([]int, 2)
	s := []int{-1, -1}
	fmt.Println(s)
	copy(s2, s)
	fmt.Println(s2)
	sliceChange(s2)
	fmt.Println(s)
}

func sliceChange(s []int) {
	s[0] = 1
	s[1] = 1
	s = append(s, 2)
	fmt.Println("change:", s)

}