判断一个 struct 是否实现了某个 interface

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type IFace iterface {
    Eat() string
}

type Bird struct {
    Eyes string
    Color int
}

var _ IFace = new(Bird)

判断一个数是否为2的n次方

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// IsPowerOfTwo reports whether given integer is a power of two.
func IsPowerOfTwo(n int) bool {
	return n&(n-1) == 0
}

print 文件调用文件的路径

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log.SetFlags(log.Llongfile)
log.Println(111)

How to best clear a slice: empty vs. nil

• yourbasic.org/golang

Remove all elements

• To remove all elements, simply set the slice to nil.

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  a := []string{"A", "B", "C", "D", "E"} a = nil fmt.Println(a, len(a), cap(a)) // [] 0 0

• This will release the underlying array to the garbage collector (assuming there are no other references).

Keep allocated memory

• To keep the underlying array, slice the slice to zero length.

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  a := []string{"A", "B", "C", "D", "E"} a = a[:0] fmt.Println(a, len(a), cap(a)) // [] 0 5

• If the slice is extended again, the original data reappears.

  1	fmt.Println(a[:2]) // [A B]

Empty slice vs. nil slice

• In practice, nil slices and empty slices can often be treated in the same way:

  • they can be used with the same effect in for loops and append functions,
  • they have zero length and capacity,
  • and they even look the same when printed.

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    var a []int = nil fmt.Println(len(a)) // 0 fmt.Println(cap(a)) // 0 fmt.Println(a) // []

• However, if needed, you can tell the difference.

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  var a []int = nil var a0 []int = make([]int, 0) fmt.Println(a == nil) // true fmt.Println(a0 == nil) // false fmt.Printf("%#v\n", a) // []int(nil) fmt.Printf("%#v\n", a0) // []int{}

• The official Go wiki recommends using nil slices over empty slices.

[…] the nil slice is the preferred style.

Note that there are limited circumstances where a non-nil but zero-length slice is preferred, such as when encoding JSON objects (a nil slice encodes to null, while []string{} encodes to the JSON array []).

When designing interfaces, avoid making a distinction between a nil slice and a non-nil, zero-length slice, as this can lead to subtle programming errors.
The Go wiki: Declaring empty slices