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// Copyright 2017, The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package value
import (
"fmt"
"math"
"reflect"
"sort"
)
// SortKeys sorts a list of map keys, deduplicating keys if necessary.
// The type of each value must be comparable.
func SortKeys(vs []reflect.Value) []reflect.Value {
if len(vs) == 0 {
return vs
}
// Sort the map keys.
sort.SliceStable(vs, func(i, j int) bool { return isLess(vs[i], vs[j]) })
// Deduplicate keys (fails for NaNs).
vs2 := vs[:1]
for _, v := range vs[1:] {
if isLess(vs2[len(vs2)-1], v) {
vs2 = append(vs2, v)
}
}
return vs2
}
// isLess is a generic function for sorting arbitrary map keys.
// The inputs must be of the same type and must be comparable.
func isLess(x, y reflect.Value) bool {
switch x.Type().Kind() {
case reflect.Bool:
return !x.Bool() && y.Bool()
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
return x.Int() < y.Int()
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
return x.Uint() < y.Uint()
case reflect.Float32, reflect.Float64:
// NOTE: This does not sort -0 as less than +0
// since Go maps treat -0 and +0 as equal keys.
fx, fy := x.Float(), y.Float()
return fx < fy || math.IsNaN(fx) && !math.IsNaN(fy)
case reflect.Complex64, reflect.Complex128:
cx, cy := x.Complex(), y.Complex()
rx, ix, ry, iy := real(cx), imag(cx), real(cy), imag(cy)
if rx == ry || (math.IsNaN(rx) && math.IsNaN(ry)) {
return ix < iy || math.IsNaN(ix) && !math.IsNaN(iy)
}
return rx < ry || math.IsNaN(rx) && !math.IsNaN(ry)
case reflect.Ptr, reflect.UnsafePointer, reflect.Chan:
return x.Pointer() < y.Pointer()
case reflect.String:
return x.String() < y.String()
case reflect.Array:
for i := 0; i < x.Len(); i++ {
if isLess(x.Index(i), y.Index(i)) {
return true
}
if isLess(y.Index(i), x.Index(i)) {
return false
}
}
return false
case reflect.Struct:
for i := 0; i < x.NumField(); i++ {
if isLess(x.Field(i), y.Field(i)) {
return true
}
if isLess(y.Field(i), x.Field(i)) {
return false
}
}
return false
case reflect.Interface:
vx, vy := x.Elem(), y.Elem()
if !vx.IsValid() || !vy.IsValid() {
return !vx.IsValid() && vy.IsValid()
}
tx, ty := vx.Type(), vy.Type()
if tx == ty {
return isLess(x.Elem(), y.Elem())
}
if tx.Kind() != ty.Kind() {
return vx.Kind() < vy.Kind()
}
if tx.String() != ty.String() {
return tx.String() < ty.String()
}
if tx.PkgPath() != ty.PkgPath() {
return tx.PkgPath() < ty.PkgPath()
}
// This can happen in rare situations, so we fallback to just comparing
// the unique pointer for a reflect.Type. This guarantees deterministic
// ordering within a program, but it is obviously not stable.
return reflect.ValueOf(vx.Type()).Pointer() < reflect.ValueOf(vy.Type()).Pointer()
default:
// Must be Func, Map, or Slice; which are not comparable.
panic(fmt.Sprintf("%T is not comparable", x.Type()))
}
}
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