Custom formatter based on go's fmt package. (#185)

* Custom formatter based on go's fmt package.

* Cleanup

* Cleanup

* Added tengo.MaxStringLen check

* Cleanup

objects/builtin_format.go

@@ -0,0 +1,27 @@
+package objects
+
+func builtinFormat(args ...Object) (Object, error) {
+	numArgs := len(args)
+	if numArgs == 0 {
+		return nil, ErrWrongNumArguments
+	}
+
+	format, ok := args[0].(*String)
+	if !ok {
+		return nil, ErrInvalidArgumentType{
+			Name:     "format",
+			Expected: "string",
+			Found:    args[0].TypeName(),
+		}
+	}
+	if numArgs == 1 {
+		return format, nil // okay to return 'format' directly as String is immutable
+	}
+
+	s, err := Format(format.Value, args[1:]...)
+	if err != nil {
+		return nil, err
+	}
+
+	return &String{Value: s}, nil
+}

objects/builtins.go

@@ -111,4 +111,8 @@ var Builtins = []*BuiltinFunction{
 		Name:  "type_name",
 		Value: builtinTypeName,
 	},
+	{
+		Name:  "format",
+		Value: builtinFormat,
+	},
 }

runtime/vm_builtin_test.go

@@ -157,6 +157,18 @@ func TestBuiltinFunction(t *testing.T) {
 	expect(t, `a := func(x) { return func() { return x } }; out = is_callable(a)`, nil, true)                              // function
 	expect(t, `a := func(x) { return func() { return x } }; out = is_callable(a(5))`, nil, true)                           // closure
 	expect(t, `out = is_callable(x)`, Opts().Symbol("x", &StringArray{Value: []string{"foo", "bar"}}).Skip2ndPass(), true) // user object
+
+	expect(t, `out = format("")`, nil, "")
+	expect(t, `out = format("foo")`, nil, "foo")
+	expect(t, `out = format("foo %d %v %s", 1, 2, "bar")`, nil, "foo 1 2 bar")
+	expect(t, `out = format("foo %v", [1, "bar", true])`, nil, `foo [1, "bar", true]`)
+	expect(t, `out = format("foo %v %d", [1, "bar", true], 19)`, nil, `foo [1, "bar", true] 19`)
+	expect(t, `out = format("foo %v", {"a": {"b": {"c": [1, 2, 3]}}})`, nil, `foo {a: {b: {c: [1, 2, 3]}}}`)
+	expect(t, `out = format("%v", [1, [2, [3, 4]]])`, nil, `[1, [2, [3, 4]]]`)
+
+	tengo.MaxStringLen = 9
+	expectError(t, `format("%s", "1234567890")`, nil, "exceeding string size limit")
+	tengo.MaxStringLen = 2147483647
 }
 
 func TestBytesN(t *testing.T) {

stdlib/fmt.go

@@ -44,17 +44,12 @@ func fmtPrintf(args ...objects.Object) (ret objects.Object, err error) {
 		return nil, nil
 	}
 
-	formatArgs := make([]interface{}, numArgs-1)
-	for idx, arg := range args[1:] {
-		switch arg := arg.(type) {
-		case *objects.Int, *objects.Float, *objects.Bool, *objects.Char, *objects.String, *objects.Bytes:
-			formatArgs[idx] = objects.ToInterface(arg)
-		default:
-			formatArgs[idx] = arg
-		}
+	s, err := objects.Format(format.Value, args[1:]...)
+	if err != nil {
+		return nil, err
 	}
 
-	fmt.Printf(format.Value, formatArgs...)
+	fmt.Print(s)
 
 	return nil, nil
 }
@@ -89,20 +84,9 @@ func fmtSprintf(args ...objects.Object) (ret objects.Object, err error) {
 		return format, nil // okay to return 'format' directly as String is immutable
 	}
 
-	formatArgs := make([]interface{}, numArgs-1)
-	for idx, arg := range args[1:] {
-		switch arg := arg.(type) {
-		case *objects.Int, *objects.Float, *objects.Bool, *objects.Char, *objects.String, *objects.Bytes:
-			formatArgs[idx] = objects.ToInterface(arg)
-		default:
-			formatArgs[idx] = arg
-		}
-	}
-
-	s := fmt.Sprintf(format.Value, formatArgs...)
-
-	if len(s) > tengo.MaxStringLen {
-		return nil, objects.ErrStringLimit
+	s, err := objects.Format(format.Value, args[1:]...)
+	if err != nil {
+		return nil, err
 	}
 
 	return &objects.String{Value: s}, nil