Implement Compare methods

The current Less implementation has an exponential complexity. Replacing
Less with a Compare method avoids that problem.

Author: apelisse

value/less_test.go

@@ -310,6 +310,19 @@ func TestValueLess(t *testing.T) {
 			if tt.b.Less(tt.b) {
 				t.Errorf("oops, b < a: %#v, %#v", tt.b, tt.a)
 			}
+
+			if tt.eq {
+				if tt.a.Compare(tt.b) != 0 || tt.b.Compare(tt.b) != 0 {
+					t.Errorf("oops, a != b: %#v, %#v", tt.a, tt.b)
+				}
+			} else {
+				if !(tt.a.Compare(tt.b) < 0) {
+					t.Errorf("oops, a is not less than b: %#v, %#v", tt.a, tt.b)
+				}
+				if !(tt.b.Compare(tt.a) > 0) {
+					t.Errorf("oops, b is not more than a: %#v, %#v", tt.a, tt.b)
+				}
+			}
 		})
 	}
 

value/value.go

@@ -98,87 +98,124 @@ func (v Value) Equals(rhs Value) bool {
 // Less provides a total ordering for Value (so that they can be sorted, even
 // if they are of different types).
 func (v Value) Less(rhs Value) bool {
+	return v.Compare(rhs) == -1
+}
+
+// Compare provides a total ordering for Value (so that they can be
+// sorted, even if they are of different types). The result will be 0 if
+// v==rhs, -1 if v < rhs, and +1 if v > rhs.
+func (v Value) Compare(rhs Value) int {
 	if v.FloatValue != nil {
 		if rhs.FloatValue == nil {
 			// Extra: compare floats and ints numerically.
 			if rhs.IntValue != nil {
-				return float64(*v.FloatValue) < float64(*rhs.IntValue)
+				return v.FloatValue.Compare(Float(*rhs.IntValue))
 			}
-			return true
+			return -1
 		}
-		return *v.FloatValue < *rhs.FloatValue
+		return v.FloatValue.Compare(*rhs.FloatValue)
 	} else if rhs.FloatValue != nil {
 		// Extra: compare floats and ints numerically.
 		if v.IntValue != nil {
-			return float64(*v.IntValue) < float64(*rhs.FloatValue)
+			return Float(*v.IntValue).Compare(*rhs.FloatValue)
 		}
-		return false
+		return 1
 	}
 
 	if v.IntValue != nil {
 		if rhs.IntValue == nil {
-			return true
+			return -1
 		}
-		return *v.IntValue < *rhs.IntValue
+		return v.IntValue.Compare(*rhs.IntValue)
 	} else if rhs.IntValue != nil {
-		return false
+		return 1
 	}
 
 	if v.StringValue != nil {
 		if rhs.StringValue == nil {
-			return true
+			return -1
 		}
-		return *v.StringValue < *rhs.StringValue
+		return strings.Compare(string(*v.StringValue), string(*rhs.StringValue))
 	} else if rhs.StringValue != nil {
-		return false
+		return 1
 	}
 
 	if v.BooleanValue != nil {
 		if rhs.BooleanValue == nil {
-			return true
-		}
-		if *v.BooleanValue == *rhs.BooleanValue {
-			return false
+			return -1
 		}
-		return *v.BooleanValue == false
+		return v.BooleanValue.Compare(*rhs.BooleanValue)
 	} else if rhs.BooleanValue != nil {
-		return false
+		return 1
 	}
 
 	if v.ListValue != nil {
 		if rhs.ListValue == nil {
-			return true
+			return -1
 		}
-		return v.ListValue.Less(rhs.ListValue)
+		return v.ListValue.Compare(rhs.ListValue)
 	} else if rhs.ListValue != nil {
-		return false
+		return 1
 	}
 	if v.MapValue != nil {
 		if rhs.MapValue == nil {
-			return true
+			return -1
 		}
-		return v.MapValue.Less(rhs.MapValue)
+		return v.MapValue.Compare(rhs.MapValue)
 	} else if rhs.MapValue != nil {
-		return false
+		return 1
 	}
 	if v.Null {
 		if !rhs.Null {
-			return true
+			return -1
 		}
-		return false
+		return 0
 	} else if rhs.Null {
-		return false
+		return 1
 	}
 
 	// Invalid Value-- nothing is set.
-	return false
+	return 0
 }
 
 type Int int64
 type Float float64
 type String string
 type Boolean bool
 
+// Compare compares integers. The result will be 0 if i==rhs, -1 if i <
+// rhs, and +1 if i > rhs.
+func (i Int) Compare(rhs Int) int {
+	if i > rhs {
+		return 1
+	} else if i < rhs {
+		return -1
+	}
+	return 0
+}
+
+// Compare compares floats. The result will be 0 if f==rhs, -1 if f <
+// rhs, and +1 if f > rhs.
+func (f Float) Compare(rhs Float) int {
+	if f > rhs {
+		return 1
+	} else if f < rhs {
+		return -1
+	}
+	return 0
+}
+
+// Compare compares booleans. The result will be 0 if b==rhs, -1 if b <
+// rhs, and +1 if b > rhs.
+func (b Boolean) Compare(rhs Boolean) int {
+	if b == rhs {
+		return 0
+	} else if b == false {
+		return -1
+	}
+	return 1
+}
+
 // Field is an individual key-value pair.
 type Field struct {
 	Name  string
@@ -206,27 +243,28 @@ func (l *List) Equals(rhs *List) bool {
 
 // Less compares two lists lexically.
 func (l *List) Less(rhs *List) bool {
+	return l.Compare(rhs) == -1
+}
+
+// Compare compares two lists lexically. The result will be 0 if l==rhs, -1
+// if l < rhs, and +1 if l > rhs.
+func (l *List) Compare(rhs *List) int {
 	i := 0
 	for {
 		if i >= len(l.Items) && i >= len(rhs.Items) {
 			// Lists are the same length and all items are equal.
-			return false
+			return 0
 		}
 		if i >= len(l.Items) {
 			// LHS is shorter.
-			return true
+			return -1
 		}
 		if i >= len(rhs.Items) {
 			// RHS is shorter.
-			return false
+			return 1
 		}
-		if l.Items[i].Less(rhs.Items[i]) {
-			// LHS is less; return
-			return true
-		}
-		if rhs.Items[i].Less(l.Items[i]) {
-			// RHS is less; return
-			return false
+		if c := l.Items[i].Compare(rhs.Items[i]); c != 0 {
+			return c
 		}
 		// The items are equal; continue.
 		i++
@@ -280,6 +318,11 @@ func (m *Map) Equals(rhs *Map) bool {
 
 // Less compares two maps lexically.
 func (m *Map) Less(rhs *Map) bool {
+	return m.Compare(rhs) == -1
+}
+
+// Compare compares two maps lexically.
+func (m *Map) Compare(rhs *Map) int {
 	var noAllocL, noAllocR [2]int
 	var morder, rorder []int
 
@@ -325,28 +368,22 @@ func (m *Map) Less(rhs *Map) bool {
 	for {
 		if i >= len(morder) && i >= len(rorder) {
 			// Maps are the same length and all items are equal.
-			return false
+			return 0
 		}
 		if i >= len(morder) {
 			// LHS is shorter.
-			return true
+			return -1
 		}
 		if i >= len(rorder) {
 			// RHS is shorter.
-			return false
+			return 1
 		}
 		fa, fb := &m.Items[morder[i]], &rhs.Items[rorder[i]]
-		if fa.Name != fb.Name {
-			// the map having the field name that sorts lexically less is "less"
-			return fa.Name < fb.Name
+		if c := strings.Compare(fa.Name, fb.Name); c != 0 {
+			return c
 		}
-		if fa.Value.Less(fb.Value) {
-			// LHS is less; return
-			return true
-		}
-		if fb.Value.Less(fa.Value) {
-			// RHS is less; return
-			return false
+		if c := fa.Value.Compare(fb.Value); c != 0 {
+			return c
 		}
 		// The items are equal; continue.
 		i++