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缘由：

Go语言中的for…range语法对于刚接触的人来说稍微有那么点不适应，容易踩坑，所以在此记录一下，方便查阅。

参考解答：

如果在range表达式的左边只有一个变量，那对应的就是下表中的「1st value」列（If only one value is used on the left of a range expression, it is the 1st value in this table.）：

Range expression	1st value	2nd value (optional)	notes
array or slice a [n]E,*[n]E, or []E	index i int	a[i] E
string s string type	index i int	rune int	range iterates over Unicode code points, not bytes
map m map[K]V	key k K	valuem[k] V
channel c chan E	elemente E	none

样例：

for k, v := range myMap {
    log.Printf("key=%v, value=%v", k, v)
}

for v := range myChannel {
    log.Printf("value=%v", v)
}

for i, v := range myArray {
    log.Printf("array value at [%d]=%v", i, v)
}

// `range` on strings iterates over Unicode code points.
// The first value is the starting byte index of the `rune` and the second the `rune` itself.
for i, c := range "go" {
    fmt.Println(i, c)
}

/* ==== */

var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
for key, value := range pow {
	fmt.Printf("%d\t%d\n", key, value)
}
for key := range pow {
	fmt.Printf("%d\t", key)
}

参考链接：

• https://gobyexample.com/range
• https://github.com/golang/go/wiki/Range
• https://tour.golang.org/moretypes/13
• http://www.cnblogs.com/howDo/archive/2013/06/01/GoLang-Control.html

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