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func main() {
	var i int
	i = 10
	fmt.Println(i)
	return
}
//➜ go run "/home/guo/code/c/main.go"
//10

func main() {
	var m map[int]int
	m[1] = 1
	fmt.Println(m[1])
	return
}
//➜ go run "/home/guo/code/c/main.go"
//panic: assignment to entry in nil map

//goroutine 1 [running]:
//main.main()
//      /home/guo/code/c/main.go:9 +0x45
//exit status 2

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package main

import "fmt"

func test_map(m map[string]string){
	fmt.Printf("inner: %v, %p\n",m, m)
	m["a"]="11"
	fmt.Printf("inner: %v, %p\n",m, m)
}

func main() {

	m := map[string]string{
		"a":"1",
		"b":"2",
		"c":"3",
	}
	
	fmt.Printf("outer: %v, %p\n",m, m)
	test_map(m)
	fmt.Printf("outer: %v, %p\n",m, m)
}

//output
//outer: map[a:1 b:2 c:3], 0x442260
//inner: map[a:1 b:2 c:3], 0x442260
//inner: map[a:11 b:2 c:3], 0x442260
//outer: map[b:2 c:3 a:11], 0x442260

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// makemap implements Go map creation for make(map[k]v, hint).
// If the compiler has determined that the map or the first bucket
// can be created on the stack, h and/or bucket may be non-nil.
// If h != nil, the map can be created directly in h.
// If h.buckets != nil, bucket pointed to can be used as the first bucket.
func makemap(t *maptype, hint int, h *hmap) *hmap {
	mem, overflow := math.MulUintptr(uintptr(hint), t.bucket.size)
	if overflow || mem > maxAlloc {
		hint = 0
	}

	// initialize Hmap
	if h == nil {
		h = new(hmap)
	}
	h.hash0 = fastrand()

	// Find the size parameter B which will hold the requested # of elements.
	// For hint < 0 overLoadFactor returns false since hint < bucketCnt.
	B := uint8(0)
	for overLoadFactor(hint, B) {
		B++
	}
	h.B = B

	// allocate initial hash table
	// if B == 0, the buckets field is allocated lazily later (in mapassign)
	// If hint is large zeroing this memory could take a while.
	if h.B != 0 {
		var nextOverflow *bmap
		h.buckets, nextOverflow = makeBucketArray(t, h.B, nil)
		if nextOverflow != nil {
			h.extra = new(mapextra)
			h.extra.nextOverflow = nextOverflow
		}
	}

	return h
}

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package main

import "fmt"


func test_chan2(ch chan string){
	fmt.Printf("inner: %v, %v\n",ch, len(ch))
	ch<-"b"
	fmt.Printf("inner: %v, %v\n",ch, len(ch))
}

func main() {
	ch := make(chan string, 10)
	ch<- "a"
	
	fmt.Printf("outer: %v, %v\n",ch, len(ch))
	test_chan2(ch)
	fmt.Printf("outer: %v, %v\n",ch, len(ch))
}
//output
//outer: 0x436100, 1
//inner: 0x436100, 1
//inner: 0x436100, 2
//outer: 0x436100, 2

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func makechan(t *chantype, size int) *hchan {
	elem := t.elem

	// compiler checks this but be safe.
	if elem.size >= 1<<16 {
		throw("makechan: invalid channel element type")
	}
	if hchanSize%maxAlign != 0 || elem.align > maxAlign {
		throw("makechan: bad alignment")
	}

	mem, overflow := math.MulUintptr(elem.size, uintptr(size))
	if overflow || mem > maxAlloc-hchanSize || size < 0 {
		panic(plainError("makechan: size out of range"))
	}

	// Hchan does not contain pointers interesting for GC when elements stored in buf do not contain pointers.
	// buf points into the same allocation, elemtype is persistent.
	// SudoG's are referenced from their owning thread so they can't be collected.
	// TODO(dvyukov,rlh): Rethink when collector can move allocated objects.
	var c *hchan
	switch {
	case mem == 0:
		// Queue or element size is zero.
		c = (*hchan)(mallocgc(hchanSize, nil, true))
		// Race detector uses this location for synchronization.
		c.buf = c.raceaddr()
	case elem.ptrdata == 0:
		// Elements do not contain pointers.
		// Allocate hchan and buf in one call.
		c = (*hchan)(mallocgc(hchanSize+mem, nil, true))
		c.buf = add(unsafe.Pointer(c), hchanSize)
	default:
		// Elements contain pointers.
		c = new(hchan)
		c.buf = mallocgc(mem, elem, true)
	}

	c.elemsize = uint16(elem.size)
	c.elemtype = elem
	c.dataqsiz = uint(size)
	lockInit(&c.lock, lockRankHchan)

	if debugChan {
		print("makechan: chan=", c, "; elemsize=", elem.size, "; dataqsiz=", size, "\n")
	}
	return c
}