「12」go 指针和引用

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今写代码时，传函数无意间想到一个问题，slice通过参数传递给函数，为何可以改变具体的值呢？

如何解决这个问题？

  • 官方查文档
  • 看源码
  • google看看有没有好的见解
  • 思考🤔+冥想🧘‍♂️

（ps:解决问题，主要不是看结果是怎么样的，主要是考虑问题的角度）

查资料

官网指南之Slice
有一段是这么描述：
Slices hold references to an underlying array, and if you assign one slice to another, both refer to the same array.

查源码

/src/runtime/slice.go

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type slice struct {
	array unsafe.Pointer  //指针类型哦
	len   int
	cap   int
}

思考

原来下层是用过array这个指针，指向具体的数据的

那么其他的引用类型呢？

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Map?
chan?
interface?
//Slice?

引用类型之Map

看源码 /src/runtime/map.go：

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// A header for a Go map.
type hmap struct {
	// Note: the format of the hmap is also encoded in cmd/compile/internal/gc/reflect.go.
	// Make sure this stays in sync with the compiler's definition.
	count     int // # live cells == size of map.  Must be first (used by len() builtin)
	flags     uint8
	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
	noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
	hash0     uint32 // hash seed

    //通过此指针类型
	buckets    unsafe.Pointer // array of 2^B Buckets. may be nil if count==0.
	oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing
	nevacuate  uintptr        // progress counter for evacuation (buckets less than this have been evacuated)

	extra *mapextra // optional fields
}

引用类型之Chan

源码:/src/runtime/chan.go

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type hchan struct {
	qcount   uint           // total data in the queue
    dataqsiz uint           // size of the circular queue
    //通过此指针类型来处理
	buf      unsafe.Pointer // points to an array of dataqsiz elements
	elemsize uint16
	closed   uint32
	elemtype *_type // element type
	sendx    uint   // send index
	recvx    uint   // receive index
	recvq    waitq  // list of recv waiters
	sendq    waitq  // list of send waiters

	// lock protects all fields in hchan, as well as several
	// fields in sudogs blocked on this channel.
	//
	// Do not change another G's status while holding this lock
	// (in particular, do not ready a G), as this can deadlock
	// with stack shrinking.
	lock mutex
}

引用类型之Interface

源码/src/runtime/runtime2.go

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type iface struct {
    tab  *itab
    //指针类型
	data unsafe.Pointer
}

type eface struct {
    _type *_type
    //指针类型
	data  unsafe.Pointer
}

结论？通过指针？

从上述源码看来，内部结构中都是用指针类型来指向具体的值，

So：形同这类的结构，肯定是引用类型的，具体是指针指向别的地址，从而来引用值。

其实这个特性很早就晓得了，只是今天又看到了，觉得还是记录着吧，也许后续哪一天就有了创新的灵感来着~~.

[睡觉了～最近有点乏～ZZzzz…]

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