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// Copyright 2009 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.
// Deep equality test via reflection
package reflect
import "unsafe"
// During deepValueEqual, must keep track of checks that are
// in progress. The comparison algorithm assumes that all
// checks in progress are true when it reencounters them.
// Visited comparisons are stored in a map indexed by visit.
type visit struct {
a1 unsafe.Pointer
a2 unsafe.Pointer
typ rawType
}
// Tests for deep equality using reflected types. The map argument tracks
// comparisons that have already been seen, which allows short circuiting on
// recursive types.
func deepValueEqual(v1, v2 Value, visited map[visit]struct{}) bool {
if !v1.IsValid() || !v2.IsValid() {
return v1.IsValid() == v2.IsValid()
}
if v1.typecode != v2.typecode {
return false
}
// We want to avoid putting more in the visited map than we need to.
// For any possible reference cycle that might be encountered,
// hard(v1, v2) needs to return true for at least one of the types in the cycle,
// and it's safe and valid to get Value's internal pointer.
hard := func(v1, v2 Value) bool {
switch v1.Kind() {
case Map, Slice, Ptr, Interface:
// Nil pointers cannot be cyclic. Avoid putting them in the visited map.
return !v1.IsNil() && !v2.IsNil()
}
return false
}
if hard(v1, v2) {
addr1 := v1.pointer()
addr2 := v2.pointer()
if uintptr(addr1) > uintptr(addr2) {
// Canonicalize order to reduce number of entries in visited.
// Assumes non-moving garbage collector.
addr1, addr2 = addr2, addr1
}
// Short circuit if references are already seen.
v := visit{addr1, addr2, v1.typecode}
if _, ok := visited[v]; ok {
return true
}
// Remember for later.
visited[v] = struct{}{}
}
switch v1.Kind() {
case Array:
for i := 0; i < v1.Len(); i++ {
if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
return false
}
}
return true
case Slice:
if v1.IsNil() != v2.IsNil() {
return false
}
if v1.Len() != v2.Len() {
return false
}
if v1.UnsafePointer() == v2.UnsafePointer() {
return true
}
for i := 0; i < v1.Len(); i++ {
if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
return false
}
}
return true
case Interface:
if v1.IsNil() || v2.IsNil() {
return v1.IsNil() == v2.IsNil()
}
return deepValueEqual(v1.Elem(), v2.Elem(), visited)
case Ptr:
if v1.UnsafePointer() == v2.UnsafePointer() {
return true
}
return deepValueEqual(v1.Elem(), v2.Elem(), visited)
case Struct:
for i, n := 0, v1.NumField(); i < n; i++ {
if !deepValueEqual(v1.Field(i), v2.Field(i), visited) {
return false
}
}
return true
case Map:
if v1.IsNil() != v2.IsNil() {
return false
}
if v1.Len() != v2.Len() {
return false
}
if v1.UnsafePointer() == v2.UnsafePointer() {
return true
}
for _, k := range v1.MapKeys() {
val1 := v1.MapIndex(k)
val2 := v2.MapIndex(k)
if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
return false
}
}
return true
case Func:
if v1.IsNil() && v2.IsNil() {
return true
}
// Can't do better than this:
return false
default:
// Normal equality suffices
return valueInterfaceUnsafe(v1) == valueInterfaceUnsafe(v2)
}
}
// DeepEqual reports whether x and y are “deeply equal”, defined as follows.
// Two values of identical type are deeply equal if one of the following cases applies.
// Values of distinct types are never deeply equal.
//
// Array values are deeply equal when their corresponding elements are deeply equal.
//
// Struct values are deeply equal if their corresponding fields,
// both exported and unexported, are deeply equal.
//
// Func values are deeply equal if both are nil; otherwise they are not deeply equal.
//
// Interface values are deeply equal if they hold deeply equal concrete values.
//
// Map values are deeply equal when all of the following are true:
// they are both nil or both non-nil, they have the same length,
// and either they are the same map object or their corresponding keys
// (matched using Go equality) map to deeply equal values.
//
// Pointer values are deeply equal if they are equal using Go's == operator
// or if they point to deeply equal values.
//
// Slice values are deeply equal when all of the following are true:
// they are both nil or both non-nil, they have the same length,
// and either they point to the same initial entry of the same underlying array
// (that is, &x[0] == &y[0]) or their corresponding elements (up to length) are deeply equal.
// Note that a non-nil empty slice and a nil slice (for example, []byte{} and []byte(nil))
// are not deeply equal.
//
// Other values - numbers, bools, strings, and channels - are deeply equal
// if they are equal using Go's == operator.
//
// In general DeepEqual is a recursive relaxation of Go's == operator.
// However, this idea is impossible to implement without some inconsistency.
// Specifically, it is possible for a value to be unequal to itself,
// either because it is of func type (uncomparable in general)
// or because it is a floating-point NaN value (not equal to itself in floating-point comparison),
// or because it is an array, struct, or interface containing
// such a value.
// On the other hand, pointer values are always equal to themselves,
// even if they point at or contain such problematic values,
// because they compare equal using Go's == operator, and that
// is a sufficient condition to be deeply equal, regardless of content.
// DeepEqual has been defined so that the same short-cut applies
// to slices and maps: if x and y are the same slice or the same map,
// they are deeply equal regardless of content.
//
// As DeepEqual traverses the data values it may find a cycle. The
// second and subsequent times that DeepEqual compares two pointer
// values that have been compared before, it treats the values as
// equal rather than examining the values to which they point.
// This ensures that DeepEqual terminates.
func DeepEqual(x, y interface{}) bool {
if x == nil || y == nil {
return x == y
}
v1 := ValueOf(x)
v2 := ValueOf(y)
if v1.typecode != v2.typecode {
return false
}
return deepValueEqual(v1, v2, make(map[visit]struct{}))
}
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