1 files changed, 126 insertions, 0 deletions
diff --git a/src/pkg/reflect/deepequal.go b/src/pkg/reflect/deepequal.go
new file mode 100644
index 000000000..a483135b0
--- /dev/null
+++ b/src/pkg/reflect/deepequal.go
@@ -0,0 +1,126 @@
+// 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
+
+// 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 are stored in a map indexed by 17 * a1 + a2;
+type visit struct {
+	a1   uintptr
+	a2   uintptr
+	typ  Type
+	next *visit
+}
+
+// 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[uintptr]*visit, depth int) (b 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
+
+	if v1.CanAddr() && v2.CanAddr() {
+		addr1 := v1.UnsafeAddr()
+		addr2 := v2.UnsafeAddr()
+		if addr1 > addr2 {
+			// Canonicalize order to reduce number of entries in visited.
+			addr1, addr2 = addr2, addr1
+		}
+
+		// Short circuit if references are identical ...
+		if addr1 == addr2 {
+			return true
+		}
+
+		// ... or already seen
+		h := 17*addr1 + addr2
+		seen := visited[h]
+		typ := v1.Type()
+		for p := seen; p != nil; p = p.next {
+			if p.a1 == addr1 && p.a2 == addr2 && p.typ == typ {
+				return true
+			}
+		}
+
+		// Remember for later.
+		visited[h] = &visit{addr1, addr2, typ, seen}
+	}
+
+	switch v1.Kind() {
+	case Array:
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		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.Len() != v2.Len() {
+			return false
+		}
+		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:
+		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.Len() != v2.Len() {
+			return false
+		}
+		for _, k := range v1.MapKeys() {
+			if !deepValueEqual(v1.MapIndex(k), v2.MapIndex(k), visited, depth+1) {
+				return false
+			}
+		}
+		return true
+	default:
+		// Normal equality suffices
+		return v1.Interface() == v2.Interface()
+	}
+
+	panic("Not reached")
+}
+
+// DeepEqual tests for deep equality. It uses normal == equality where possible
+// but will scan members of arrays, slices, and fields of structs. It correctly
+// handles recursive types.
+func DeepEqual(a1, a2 interface{}) bool {
+	if a1 == nil || a2 == nil {
+		return a1 == a2
+	}
+	v1 := ValueOf(a1)
+	v2 := ValueOf(a2)
+	if v1.Type() != v2.Type() {
+		return false
+	}
+	return deepValueEqual(v1, v2, make(map[uintptr]*visit), 0)
+}