[1/7] Preprocessor cleanup

[official-gcc.git] / libgo / go / reflect / deepequal.go

// 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(val1, val2, 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)
}