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|
package seq
import (
"fmt"
"reflect"
"sort"
)
// Compare returns 0 if a and b are equal, -1 if a < b, or 1 if a > b.
// Panics if a and b are not of the same type, or are of a type not listed here.
// * Bools are compared assuming false < true.
// * Strings, integer and float values are compared as Go compares them.
// * Two nil pointers are equal; one nil pointer is treated as smaller than a non-nil pointer.
// * Non-nil pointers are compared by comparing the values they point to.
// * Structures are compared by comparing their fields in order.
// * Slices are compared by comparing elements sequentially. If the slices are of different
// length and all elements are the same up to the shorter length, the shorter slice is treated as
// smaller.
// * Maps can only be compared if they have string keys, in which case the ordered list of
// keys are first compared as string slices, and if they're equal then the values are compared
// sequentially in key order.
func Compare(a, b interface{}) int {
return compareValue(reflect.ValueOf(a), reflect.ValueOf(b))
}
func boolToInt(b bool) int {
if b {
return 1
}
return 0
}
func compareValue(ir1, ir2 reflect.Value) int {
var zerovalue reflect.Value
r1, r2 := reflect.Indirect(ir1), reflect.Indirect(ir2)
if r1 == zerovalue {
if r2 == zerovalue {
return 0
}
return -1
}
if r2 == zerovalue {
return 1
}
switch r1.Kind() {
case reflect.Bool:
v1, v2 := boolToInt(r1.Bool()), boolToInt(r2.Bool())
if v1 < v2 {
return -1
}
if v1 > v2 {
return 1
}
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
v1, v2 := r1.Int(), r2.Int()
if v1 < v2 {
return -1
}
if v1 > v2 {
return 1
}
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
v1, v2 := r1.Uint(), r2.Uint()
if v1 < v2 {
return -1
}
if v1 > v2 {
return 1
}
case reflect.Float32, reflect.Float64:
v1, v2 := r1.Float(), r2.Float()
if v1 < v2 {
return -1
}
if v1 > v2 {
return 1
}
case reflect.Map:
return compareMap(r1, r2)
case reflect.Struct:
return compareStruct(r1, r2)
case reflect.Slice:
if r1.Type().Elem().Kind() == reflect.Uint8 {
// Not using bytes.Compare because that fails on unexported fields:
// return bytes.Compare(r1.Interface().([]byte), r2.Interface().([]byte))
var s string
strtype := reflect.TypeOf(s)
v1, v2 := r1.Convert(strtype).String(), r2.Convert(strtype).String()
if v1 < v2 {
return -1
}
if v1 > v2 {
return 1
}
}
return compareSlice(r1, r2)
case reflect.String:
v1, v2 := r1.String(), r2.String()
if v1 < v2 {
return -1
}
if v1 > v2 {
return 1
}
default:
panic(fmt.Sprintf("don't know how to compare values of type %v", r1.Type()))
}
return 0
}
func compareStruct(r1, r2 reflect.Value) int {
if r1.Type() != r2.Type() {
panic(fmt.Sprintf("s1 and s2 are not of the same type: %v, %v", r1.Type(), r2.Type()))
}
n := r1.NumField()
for i := 0; i < n; i++ {
c := compareValue(r1.Field(i), r2.Field(i))
if c != 0 {
return c
}
}
return 0
}
func compareSlice(r1, r2 reflect.Value) int {
maxlen := r1.Len()
if r2.Len() < maxlen {
maxlen = r2.Len()
}
for i := 0; i < maxlen; i++ {
c := compareValue(r1.Index(i), r2.Index(i))
if c != 0 {
return c
}
}
if r1.Len() > maxlen {
return 1
}
if r2.Len() > maxlen {
return -1
}
return 0
}
func sortedKeys(r1 reflect.Value) []string {
keys := make([]string, 0, r1.Len())
for _, k := range r1.MapKeys() {
keys = append(keys, k.String())
}
sort.Strings(keys)
return keys
}
func compareMap(r1, r2 reflect.Value) int {
if r1.Type().Key().Kind() != reflect.String {
panic("can only compare maps with keys of type string")
}
s1, s2 := sortedKeys(r1), sortedKeys(r2)
c := compareSlice(reflect.ValueOf(s1), reflect.ValueOf(s2))
if c != 0 {
return c
}
for _, k := range s1 {
vk := reflect.ValueOf(k)
c := compareValue(r1.MapIndex(vk), r2.MapIndex(vk))
if c != 0 {
return c
}
}
return 0
}
|
