golang sort.Slice

sort.Slice是golang提供的切片排序方法，

1. 其中使用到了反射（reflect）包

241 // Slice sorts the provided slice given the provided less function.242 //243 // The sort is not guaranteed to be stable. For a stable sort, use244 // SliceStable.245 //246 // The function panics if the provided interface is not a slice.247 func Slice(slice interface{}, less func(i, j int) bool) {248     rv := reflect.ValueOf(slice) 249     swap := reflect.Swapper(slice)250     length := rv.Len()251     quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))252 }

2. 使用了閉包

swap := reflect.Swapper(slice)// Swapper returns a function that swaps the elements in the provided 10 // slice. 11 // 12 // Swapper panics if the provided interface is not a slice. 13 func Swapper(slice interface{}) func(i, j int) { 14     v := ValueOf(slice) 15     if v.Kind() != Slice { 16         panic(&ValueError{Method: "Swapper", Kind: v.Kind()}) 17     }..................此處省略部分代碼 62     tmp := unsafe_New(typ) // swap scratch space 63 64     return func(i, j int) { 65         if uint(i) >= uint(s.Len) || uint(j) >= uint(s.Len) { 66             panic("reflect: slice index out of range") 67         } 68         val1 := arrayAt(s.Data, i, size) 69         val2 := arrayAt(s.Data, j, size) 70         typedmemmove(typ, tmp, val1) 71         typedmemmove(typ, val1, val2) 72         typedmemmove(typ, val2, tmp) 73     } 74 }

3. 可以參考何時使用panic

250     length := rv.Len()1019 // Len returns v's length.1020 // It panics if v's Kind is not Array, Chan, Map, Slice, or String.1021 func (v Value) Len() int {1022     k := v.kind()1023     switch k {1024     case Array:1025         tt := (*arrayType)(unsafe.Pointer(v.typ))1026         return int(tt.len)1027     case Chan:1028         return chanlen(v.pointer())1029     case Map:1030         return maplen(v.pointer())1031     case Slice:1032         // Slice is bigger than a word; assume flagIndir.1033         return (*sliceHeader)(v.ptr).Len1034     case String:1035         // String is bigger than a word; assume flagIndir.1036         return (*stringHeader)(v.ptr).Len1037     }1038     panic(&ValueError{"reflect.Value.Len", v.kind()})1039 }

4. quickSort函數設計學習，同時使用了heapsort、insertionSort和單次希爾排序

135 // Auto-generated variant of sort.go:quickSort136 func quickSort_func(data lessSwap, a, b, maxDepth int) {137     for b-a > 12 {138         if maxDepth == 0 {139             heapSort_func(data, a, b)140             return141         }142         maxDepth--143         mlo, mhi := doPivot_func(data, a, b)144         if mlo-a < b-mhi {145             quickSort_func(data, a, mlo, maxDepth)146             a = mhi147         } else {148             quickSort_func(data, mhi, b, maxDepth)149             b = mlo150         }151     }152     if b-a > 1 {153         for i := a + 6; i < b; i++ {154             if data.Less(i, i-6) {155                 data.Swap(i, i-6)156             }157         }158         insertionSort_func(data, a, b)159     }160 }

5. 合法性處理

// Swapper returns a function that swaps the elements in the provided 10 // slice. 11 // 12 // Swapper panics if the provided interface is not a slice. 13 func Swapper(slice interface{}) func(i, j int) { 14    ...........省略部分代碼 18     // Fast path for slices of size 0 and 1. Nothing to swap. 19     switch v.Len() { 20     case 0: 21         return func(i, j int) { panic("reflect: slice index out of range") } 22     case 1: 23         return func(i, j int) { 24             if i != 0 || j != 0 { 25                 panic("reflect: slice index out of range") 26             } 27         } 28     }