deepequal.go

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Deep equality test via reflection
     6  
     7  package reflect
     8  
     9  import (
    10  	"internal/bytealg"
    11  	"unsafe"
    12  )
    13  
    14  // During deepValueEqual, must keep track of checks that are
    15  // in progress. The comparison algorithm assumes that all
    16  // checks in progress are true when it reencounters them.
    17  // Visited comparisons are stored in a map indexed by visit.
    18  type visit struct {
    19  	a1  unsafe.Pointer
    20  	a2  unsafe.Pointer
    21  	typ Type
    22  }
    23  
    24  // Tests for deep equality using reflected types. The map argument tracks
    25  // comparisons that have already been seen, which allows short circuiting on
    26  // recursive types.
    27  func deepValueEqual(v1, v2 Value, visited map[visit]bool) bool {
    28  	if !v1.IsValid() || !v2.IsValid() {
    29  		return v1.IsValid() == v2.IsValid()
    30  	}
    31  	if v1.Type() != v2.Type() {
    32  		return false
    33  	}
    34  
    35  	// We want to avoid putting more in the visited map than we need to.
    36  	// For any possible reference cycle that might be encountered,
    37  	// hard(v1, v2) needs to return true for at least one of the types in the cycle,
    38  	// and it's safe and valid to get Value's internal pointer.
    39  	hard := func(v1, v2 Value) bool {
    40  		switch v1.Kind() {
    41  		case Pointer:
    42  			if !v1.typ().Pointers() {
    43  				// not-in-heap pointers can't be cyclic.
    44  				// At least, all of our current uses of internal/runtime/sys.NotInHeap
    45  				// have that property. The runtime ones aren't cyclic (and we don't use
    46  				// DeepEqual on them anyway), and the cgo-generated ones are
    47  				// all empty structs.
    48  				return false
    49  			}
    50  			fallthrough
    51  		case Map, Slice, Interface:
    52  			// Nil pointers cannot be cyclic. Avoid putting them in the visited map.
    53  			return !v1.IsNil() && !v2.IsNil()
    54  		}
    55  		return false
    56  	}
    57  
    58  	if hard(v1, v2) {
    59  		// For a Pointer or Map value, we need to check flagIndir,
    60  		// which we do by calling the pointer method.
    61  		// For Slice or Interface, flagIndir is always set,
    62  		// and using v.ptr suffices.
    63  		ptrval := func(v Value) unsafe.Pointer {
    64  			switch v.Kind() {
    65  			case Pointer, Map:
    66  				return v.pointer()
    67  			default:
    68  				return v.ptr
    69  			}
    70  		}
    71  		addr1 := ptrval(v1)
    72  		addr2 := ptrval(v2)
    73  		if uintptr(addr1) > uintptr(addr2) {
    74  			// Canonicalize order to reduce number of entries in visited.
    75  			// Assumes non-moving garbage collector.
    76  			addr1, addr2 = addr2, addr1
    77  		}
    78  
    79  		// Short circuit if references are already seen.
    80  		typ := v1.Type()
    81  		v := visit{addr1, addr2, typ}
    82  		if visited[v] {
    83  			return true
    84  		}
    85  
    86  		// Remember for later.
    87  		visited[v] = true
    88  	}
    89  
    90  	switch v1.Kind() {
    91  	case Array:
    92  		for i := 0; i < v1.Len(); i++ {
    93  			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
    94  				return false
    95  			}
    96  		}
    97  		return true
    98  	case Slice:
    99  		if v1.IsNil() != v2.IsNil() {
   100  			return false
   101  		}
   102  		if v1.Len() != v2.Len() {
   103  			return false
   104  		}
   105  		if v1.UnsafePointer() == v2.UnsafePointer() {
   106  			return true
   107  		}
   108  		// Special case for []byte, which is common.
   109  		if v1.Type().Elem().Kind() == Uint8 {
   110  			return bytealg.Equal(v1.Bytes(), v2.Bytes())
   111  		}
   112  		for i := 0; i < v1.Len(); i++ {
   113  			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
   114  				return false
   115  			}
   116  		}
   117  		return true
   118  	case Interface:
   119  		if v1.IsNil() || v2.IsNil() {
   120  			return v1.IsNil() == v2.IsNil()
   121  		}
   122  		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
   123  	case Pointer:
   124  		if v1.UnsafePointer() == v2.UnsafePointer() {
   125  			return true
   126  		}
   127  		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
   128  	case Struct:
   129  		for i, n := 0, v1.NumField(); i < n; i++ {
   130  			if !deepValueEqual(v1.Field(i), v2.Field(i), visited) {
   131  				return false
   132  			}
   133  		}
   134  		return true
   135  	case Map:
   136  		if v1.IsNil() != v2.IsNil() {
   137  			return false
   138  		}
   139  		if v1.Len() != v2.Len() {
   140  			return false
   141  		}
   142  		if v1.UnsafePointer() == v2.UnsafePointer() {
   143  			return true
   144  		}
   145  		iter := v1.MapRange()
   146  		for iter.Next() {
   147  			val1 := iter.Value()
   148  			val2 := v2.MapIndex(iter.Key())
   149  			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
   150  				return false
   151  			}
   152  		}
   153  		return true
   154  	case Func:
   155  		if v1.IsNil() && v2.IsNil() {
   156  			return true
   157  		}
   158  		// Can't do better than this:
   159  		return false
   160  	case Int, Int8, Int16, Int32, Int64:
   161  		return v1.Int() == v2.Int()
   162  	case Uint, Uint8, Uint16, Uint32, Uint64, Uintptr:
   163  		return v1.Uint() == v2.Uint()
   164  	case String:
   165  		return v1.String() == v2.String()
   166  	case Bool:
   167  		return v1.Bool() == v2.Bool()
   168  	case Float32, Float64:
   169  		return v1.Float() == v2.Float()
   170  	case Complex64, Complex128:
   171  		return v1.Complex() == v2.Complex()
   172  	default:
   173  		// Normal equality suffices
   174  		return valueInterface(v1, false) == valueInterface(v2, false)
   175  	}
   176  }
   177  
   178  // DeepEqual reports whether x and y are “deeply equal,” defined as follows.
   179  // Two values of identical type are deeply equal if one of the following cases applies.
   180  // Values of distinct types are never deeply equal.
   181  //
   182  // Array values are deeply equal when their corresponding elements are deeply equal.
   183  //
   184  // Struct values are deeply equal if their corresponding fields,
   185  // both exported and unexported, are deeply equal.
   186  //
   187  // Func values are deeply equal if both are nil; otherwise they are not deeply equal.
   188  //
   189  // Interface values are deeply equal if they hold deeply equal concrete values.
   190  //
   191  // Map values are deeply equal when all of the following are true:
   192  // they are both nil or both non-nil, they have the same length,
   193  // and either they are the same map object or their corresponding keys
   194  // (matched using Go equality) map to deeply equal values.
   195  //
   196  // Pointer values are deeply equal if they are equal using Go's == operator
   197  // or if they point to deeply equal values.
   198  //
   199  // Slice values are deeply equal when all of the following are true:
   200  // they are both nil or both non-nil, they have the same length,
   201  // and either they point to the same initial entry of the same underlying array
   202  // (that is, &x[0] == &y[0]) or their corresponding elements (up to length) are deeply equal.
   203  // Note that a non-nil empty slice and a nil slice (for example, []byte{} and []byte(nil))
   204  // are not deeply equal.
   205  //
   206  // Other values - numbers, bools, strings, and channels - are deeply equal
   207  // if they are equal using Go's == operator.
   208  //
   209  // In general DeepEqual is a recursive relaxation of Go's == operator.
   210  // However, this idea is impossible to implement without some inconsistency.
   211  // Specifically, it is possible for a value to be unequal to itself,
   212  // either because it is of func type (uncomparable in general)
   213  // or because it is a floating-point NaN value (not equal to itself in floating-point comparison),
   214  // or because it is an array, struct, or interface containing
   215  // such a value.
   216  // On the other hand, pointer values are always equal to themselves,
   217  // even if they point at or contain such problematic values,
   218  // because they compare equal using Go's == operator, and that
   219  // is a sufficient condition to be deeply equal, regardless of content.
   220  // DeepEqual has been defined so that the same short-cut applies
   221  // to slices and maps: if x and y are the same slice or the same map,
   222  // they are deeply equal regardless of content.
   223  //
   224  // As DeepEqual traverses the data values it may find a cycle. The
   225  // second and subsequent times that DeepEqual compares two pointer
   226  // values that have been compared before, it treats the values as
   227  // equal rather than examining the values to which they point.
   228  // This ensures that DeepEqual terminates.
   229  func DeepEqual(x, y any) bool {
   230  	if x == nil || y == nil {
   231  		return x == y
   232  	}
   233  	v1 := ValueOf(x)
   234  	v2 := ValueOf(y)
   235  	if v1.Type() != v2.Type() {
   236  		return false
   237  	}
   238  	return deepValueEqual(v1, v2, make(map[visit]bool))
   239  }
   240
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