builtin: add an Option2 struct (#8890)

examples/eventbus/eventbus.v

@@ -8,6 +8,6 @@ fn main(){
 	some_module.do_work()
 }
 
-fn on_error(sender voidptr, e &some_module.Error, x voidptr) {
+fn on_error(sender voidptr, e &some_module.MyError, x voidptr) {
 	println(e.message)
 }

examples/eventbus/modules/some_module/some_module.v

@@ -11,7 +11,7 @@ pub struct Work {
 	hours int
 }
 
-pub struct Error {
+pub struct MyError {
 pub:
 	message string
 }
@@ -21,7 +21,7 @@ pub fn do_work(){
 	for i in 0..20 {
 		println("working...")
 		if i == 15 {
-			error := &Error{"There was an error."}
+			error := &MyError{"There was an error."}
 			eb.publish("error", work, error)
 			eb.publish("error", work, error)
 			return

vlib/builtin/option.v

@@ -3,16 +3,6 @@
 // that can be found in the LICENSE file.
 module builtin
 
-/*
-struct Option2<T> {
-	ok bool
-	is_none bool
-	error string
-	ecode int
-	data T
-}
-*/
-// OptionBase is the the base of V's internal optional return system.
 struct OptionBase {
 	ok      bool
 	is_none bool
@@ -81,3 +71,65 @@ pub fn error_with_code(message string, code int) Option {
 		ecode: code
 	}
 }
+
+struct Option2 {
+	state byte
+	err   Error
+}
+
+// OptionBase is the the base of V's internal optional return system.
+struct OptionBase2 {
+	state byte
+	err   Error
+	// Data is trailing after err
+	// and is not included in here but in the
+	// derived Option2_xxx types
+}
+
+// Error holds information about an error instance
+struct Error {
+	msg  string
+	code int
+}
+
+// /*
+pub fn (o Option2) str() string {
+	if o.state == 0 {
+		return 'Option2{ ok }'
+	}
+	if o.state == 1 {
+		return 'Option2{ none }'
+	}
+	return 'Option2{ err: "$o.err.msg" }'
+}
+
+// opt_none is used internally when returning `none`.
+fn opt_none2() Option2 {
+	return Option2{
+		state: 1
+	}
+}
+
+// error returns an optional containing the error given in `message`.
+// `if ouch { return error('an error occurred') }`
+pub fn error2(message string) Option2 {
+	return Option2{
+		state: 2
+		err: {
+			msg: message
+		}
+	}
+}
+
+// error_with_code returns an optional containing both error `message` and error `code`.
+// `if ouch { return error_with_code('an error occurred',1) }`
+pub fn error_with_code2(message string, code int) Option2 {
+	return Option2{
+		state: 2
+		err: {
+			msg: message
+			code: code
+		}
+	}
+}
+// */

vlib/v/checker/checker.v

@@ -2355,7 +2355,8 @@ pub fn (mut c Checker) return_stmt(mut return_stmt ast.Return) {
 	}
 	return_stmt.types = got_types
 	// allow `none` & `error (Option)` return types for function that returns optional
-	if exp_is_optional && got_types[0].idx() in [table.none_type_idx, c.table.type_idxs['Option']] {
+	if exp_is_optional
+		&& got_types[0].idx() in [table.none_type_idx, c.table.type_idxs['Option'], c.table.type_idxs['Option2']] {
 		return
 	}
 	if expected_types.len > 0 && expected_types.len != got_types.len {

vlib/v/gen/c/cgen.v

@@ -5286,7 +5286,7 @@ fn (mut g Gen) write_init_function() {
 }
 
 const (
-	builtins = ['string', 'array', 'KeyValue', 'DenseArray', 'map', 'Option']
+	builtins = ['string', 'array', 'KeyValue', 'DenseArray', 'map', 'Option', 'Error', 'Option2']
 )
 
 fn (mut g Gen) write_builtin_types() {