Add ability to use operator overloading with methods

Author: antonmedv

checker/checker.go

@@ -176,9 +176,12 @@ func (v *visitor) BinaryNode(node *ast.BinaryNode) reflect.Type {
 	if fns, ok := v.operators[node.Operator]; ok {
 		for _, fn := range fns {
 			fnType := v.types[fn]
-
-			firstArgType := fnType.Type.In(0)
-			secondArgType := fnType.Type.In(1)
+			firstInIndex := 0
+			if fnType.Method {
+				firstInIndex = 1 // As first argument to method is receiver.
+			}
+			firstArgType := fnType.Type.In(firstInIndex)
+			secondArgType := fnType.Type.In(firstInIndex + 1)
 
 			if l == firstArgType && r == secondArgType {
 				return fnType.Type.Out(0)

checker/patcher.go

@@ -27,9 +27,12 @@ func (p *operatorPatcher) Exit(node *ast.Node) {
 	rightType := binaryNode.Right.GetType()
 	for _, fn := range fns {
 		fnType := p.types[fn]
-
-		firstArgType := fnType.Type.In(0)
-		secondArgType := fnType.Type.In(1)
+		firstInIndex := 0
+		if fnType.Method {
+			firstInIndex = 1 // As first argument to method is receiver.
+		}
+		firstArgType := fnType.Type.In(firstInIndex)
+		secondArgType := fnType.Type.In(firstInIndex + 1)
 
 		if leftType == firstArgType && rightType == secondArgType {
 			newNode := &ast.FunctionNode{

expr_test.go

@@ -401,6 +401,21 @@ func ExampleEval_marshal() {
 	// Output: true
 }
 
+func TestOperator_struct(t *testing.T) {
+	env := &mockEnv{
+		BirthDay: time.Date(2017, time.October, 23, 18, 30, 0, 0, time.UTC),
+	}
+
+	code := `BirthDay == "2017-10-23"`
+
+	program, err := expr.Compile(code, expr.Env(&mockEnv{}), expr.Operator("==", "DateEqual"))
+	require.NoError(t, err)
+
+	output, err := expr.Run(program, env)
+	require.NoError(t, err)
+	require.Equal(t, true, output)
+}
+
 func TestExpr(t *testing.T) {
 	env := &mockEnv{
 		Any:     "any",
@@ -817,6 +832,10 @@ func (*mockEnv) MapArg(m map[string]interface{}) string {
 	return m["foo"].(string)
 }
 
+func (*mockEnv) DateEqual(date time.Time, s string) bool {
+	return date.Format("2006-01-02") == s
+}
+
 type ticket struct {
 	Price int
 }

internal/conf/config.go

@@ -36,8 +36,11 @@ func (c *Config) Check() error {
 			if !ok || fnType.Type.Kind() != reflect.Func {
 				return fmt.Errorf("function %s for %s operator does not exist in environment", fn, op)
 			}
-
-			if fnType.Type.NumIn() != 2 || fnType.Type.NumOut() != 1 {
+			requiredNumIn := 2
+			if fnType.Method {
+				requiredNumIn = 3 // As first argument of method is receiver.
+			}
+			if fnType.Type.NumIn() != requiredNumIn || fnType.Type.NumOut() != 1 {
 				return fmt.Errorf("function %s for %s operator does not have a correct signature", fn, op)
 			}
 		}