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Source file src/reflect/deepequal.go

Documentation: reflect

  // 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 Type
  }
  
  // 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]bool, depth int) bool {
  	if !v1.IsValid() || !v2.IsValid() {
  		return v1.IsValid() == v2.IsValid()
  	}
  	if v1.Type() != v2.Type() {
  		return false
  	}
  
  	// if depth > 10 { panic("deepValueEqual") }	// for debugging
  
  	// We want to avoid putting more in the visited map than we need to.
  	// For any possible reference cycle that might be encountered,
  	// hard(t) needs to return true for at least one of the types in the cycle.
  	hard := func(k Kind) bool {
  		switch k {
  		case Map, Slice, Ptr, Interface:
  			return true
  		}
  		return false
  	}
  
  	if v1.CanAddr() && v2.CanAddr() && hard(v1.Kind()) {
  		addr1 := unsafe.Pointer(v1.UnsafeAddr())
  		addr2 := unsafe.Pointer(v2.UnsafeAddr())
  		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.
  		typ := v1.Type()
  		v := visit{addr1, addr2, typ}
  		if visited[v] {
  			return true
  		}
  
  		// Remember for later.
  		visited[v] = true
  	}
  
  	switch v1.Kind() {
  	case Array:
  		for i := 0; i < v1.Len(); i++ {
  			if !deepValueEqual(v1.Index(i), v2.Index(i), visited, depth+1) {
  				return false
  			}
  		}
  		return true
  	case Slice:
  		if v1.IsNil() != v2.IsNil() {
  			return false
  		}
  		if v1.Len() != v2.Len() {
  			return false
  		}
  		if v1.Pointer() == v2.Pointer() {
  			return true
  		}
  		for i := 0; i < v1.Len(); i++ {
  			if !deepValueEqual(v1.Index(i), v2.Index(i), visited, depth+1) {
  				return false
  			}
  		}
  		return true
  	case Interface:
  		if v1.IsNil() || v2.IsNil() {
  			return v1.IsNil() == v2.IsNil()
  		}
  		return deepValueEqual(v1.Elem(), v2.Elem(), visited, depth+1)
  	case Ptr:
  		if v1.Pointer() == v2.Pointer() {
  			return true
  		}
  		return deepValueEqual(v1.Elem(), v2.Elem(), visited, depth+1)
  	case Struct:
  		for i, n := 0, v1.NumField(); i < n; i++ {
  			if !deepValueEqual(v1.Field(i), v2.Field(i), visited, depth+1) {
  				return false
  			}
  		}
  		return true
  	case Map:
  		if v1.IsNil() != v2.IsNil() {
  			return false
  		}
  		if v1.Len() != v2.Len() {
  			return false
  		}
  		if v1.Pointer() == v2.Pointer() {
  			return true
  		}
  		for _, k := range v1.MapKeys() {
  			val1 := v1.MapIndex(k)
  			val2 := v2.MapIndex(k)
  			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(v1.MapIndex(k), v2.MapIndex(k), visited, depth+1) {
  				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 valueInterface(v1, false) == valueInterface(v2, false)
  	}
  }
  
  // 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.Type() != v2.Type() {
  		return false
  	}
  	return deepValueEqual(v1, v2, make(map[visit]bool), 0)
  }
  

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