为什么大厂都在用 GO 语言？读透 GO 语言的切片

package main
import ("fmt")
func main() {
var a []int //定义一个切片fmt.Printf("len: %d  cap: %d pointer: %p\n", len(a), cap(a), a)//此时切片长度和容量都是0，运行结果为len: 0  cap: 0 pointer: 0x0a = append(a, 1) // 追加1个元素fmt.Printf("len: %d  cap: %d pointer: %p\n", len(a), cap(a), a)//注意此时a的地址已经发生变化为新的切片了，新切片长度和容量都为1运行结果为：len: 1  cap: 1 pointer: 0xc000072098a = append(a, 2, 3, 4) // 追加多个元素fmt.Printf("len: %d  cap: %d pointer: %p\n", len(a), cap(a), a)//注意此时a的地址再次发生变化实际上又生成为新的切片了，新切片长度和容量都为4运行结果为：len: 4  cap: 4 pointer: 0xc000070160a = append(a, 5) // 再追加一个元素fmt.Printf("len: %d  cap: %d pointer: %p\n", len(a), cap(a), a)//注意切片扩容策略是倍增方式容量由4变成8，而长度是5运行结果为：len: 4  cap: 4 pointer: 0xc000070160
}

package main

import ("fmt")
func main() {var a = []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10} //使用原始定义法来声明并初始化一个切片fmt.Println(a)                               //运行结果为[1 2 3 4 5 6 7 8 9 10]a = a[1:]                                    // 删除第1个元素fmt.Println(a)                               //删头第1个元素后，运行结果为[2 3 4 5 6 7 8 9 10]a = a[2:]                                    // 删除前2个元素fmt.Println(a)                               //删头前2个元素后，运行结果为[4 5 6 7 8 9 10]
}

type slice struct {
array unsafe.Pointer    len   int    cap   int}

func makeslice(et *_type, len, cap int) slice {
     mem, overflow := math.MulUintptr(et.size, uintptr(cap))//此函数计算et.size也就是每个元素所占空间的大小，并与容量cap相乘，其中mem既为所需要最大内存，overflow代表是否会造成溢出if overflow || mem > maxAlloc || len < 0 || len > cap {//判断是否有溢出，长度为负数或者长度比容量大的情况，如存在 直接panic// NOTE: Produce a 'len out of range' error instead of a// 'cap out of range' error when someone does make([]T, bignumber).// 'cap out of range' is true too, but since the cap is only being// supplied implicitly, saying len is clearer.// See 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)// 如果错误检查成功，则分配内存，注意slice对象会被GC所自动清除。
}

func growslice(et *_type, old slice, cap int) slice {

// 单纯地扩容，不写数据    if et.size == 0 {        if cap < old.cap {            panic(errorString("growslice: cap out of range"))        }        // 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}    }// 扩容规则 1.新的容量大于旧的2倍，直接扩容至新的容量// 2.新的容量不大于旧的2倍，当旧的长度小于1024时，扩容至旧的2倍，否则扩容至旧的1.25倍    newcap := old.cap    doublecap := newcap + newcap    if cap > doublecap {        newcap = cap    } else {        if old.len < 1024 {            newcap = doublecap        } else {            for newcap < cap {                newcap += newcap / 4            }        }    }
// 跟据切片类型和容量计算要分配内存的大小
var overflow boolvar lenmem, newlenmem, capmem uintptr    switch {case et.size == 1:lenmem = uintptr(old.len)newlenmem = uintptr(cap)capmem = roundupsize(uintptr(newcap))overflow = uintptr(newcap) > maxAllocnewcap = int(capmem)case et.size == sys.PtrSize:lenmem = uintptr(old.len) * sys.PtrSizenewlenmem = uintptr(cap) * sys.PtrSizecapmem = roundupsize(uintptr(newcap) * sys.PtrSize)overflow = uintptr(newcap) > maxAlloc/sys.PtrSizenewcap = int(capmem / sys.PtrSize)case isPowerOfTwo(et.size):var shift uintptrif 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) << shiftnewlenmem = uintptr(cap) << shiftcapmem = roundupsize(uintptr(newcap) << shift)overflow = uintptr(newcap) > (maxAlloc >> shift)newcap = int(capmem >> shift)default:lenmem = uintptr(old.len) * et.sizenewlenmem = uintptr(cap) * et.sizecapmem, overflow = math.MulUintptr(et.size, uintptr(newcap))capmem = roundupsize(capmem)newcap = int(capmem / et.size)}// 异常情况，旧的容量比新的容量还大或者新的容量超过限制了    if cap < old.cap || uintptr(newcap) > maxSliceCap(et.size) {        panic(errorString("growslice: cap out of range"))    }
    var p unsafe.Pointer    if et.kind&kindNoPointers != 0 {
// 为新的切片开辟容量为capmem的地址空间        p = mallocgc(capmem, nil, false)// 将旧切片的数据搬到新切片开辟的地址中        memmove(p, old.array, lenmem)        // 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.// 清理下新切片中剩余地址，不能存放堆栈指针
// memclrNoHeapPointers clears n bytes starting at ptr.//// Usually you should use typedmemclr. memclrNoHeapPointers should be// used only when the caller knows that *ptr contains no heap pointers// because either://// 1. *ptr is initialized memory and its type is pointer-free.//// 2. *ptr is uninitialized memory (e.g., memory that's being reused//    for a new allocation) and hence contains only "junk".        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 !writeBarrier.enabled {            memmove(p, old.array, lenmem)        } else {            for i := uintptr(0); i < lenmem; i += et.size {                typedmemmove(et, add(p, i), add(old.array, i))            }        }    }
    return slice{p, old.len, newcap}}