[go-experimental] Add convenience wrapper function for oneOf members (#6316)

modules/openapi-generator/src/main/resources/go-experimental/model_oneof.mustache

@@ -5,6 +5,14 @@ type {{classname}} struct {
 	{{/oneOf}}
 }
 
+{{#oneOf}}
+// {{{.}}}As{{classname}} is a convenience function that returns {{{.}}} wrapped in {{classname}}
+func {{{.}}}As{{classname}}(v *{{{.}}}) {{classname}} {
+    return {{classname}}{ {{{.}}}: v}
+}
+
+{{/oneOf}}
+
 // Unmarshl JSON data into one of the pointers in the struct
 func (dst *{{classname}}) UnmarshalJSON(data []byte) error {
 	var err error

samples/openapi3/client/petstore/go-experimental/go-petstore/model_fruit.go

@@ -20,6 +20,17 @@ type Fruit struct {
 	Banana *Banana
 }
 
+// AppleAsFruit is a convenience function that returns Apple wrapped in Fruit
+func AppleAsFruit(v *Apple) Fruit {
+    return Fruit{ Apple: v}
+}
+
+// BananaAsFruit is a convenience function that returns Banana wrapped in Fruit
+func BananaAsFruit(v *Banana) Fruit {
+    return Fruit{ Banana: v}
+}
+
+
 // Unmarshl JSON data into one of the pointers in the struct
 func (dst *Fruit) UnmarshalJSON(data []byte) error {
 	var err error

samples/openapi3/client/petstore/go-experimental/go-petstore/model_fruit_req.go

@@ -20,6 +20,17 @@ type FruitReq struct {
 	BananaReq *BananaReq
 }
 
+// AppleReqAsFruitReq is a convenience function that returns AppleReq wrapped in FruitReq
+func AppleReqAsFruitReq(v *AppleReq) FruitReq {
+    return FruitReq{ AppleReq: v}
+}
+
+// BananaReqAsFruitReq is a convenience function that returns BananaReq wrapped in FruitReq
+func BananaReqAsFruitReq(v *BananaReq) FruitReq {
+    return FruitReq{ BananaReq: v}
+}
+
+
 // Unmarshl JSON data into one of the pointers in the struct
 func (dst *FruitReq) UnmarshalJSON(data []byte) error {
 	var err error

samples/openapi3/client/petstore/go-experimental/go-petstore/model_mammal.go

@@ -20,6 +20,17 @@ type Mammal struct {
 	Zebra *Zebra
 }
 
+// WhaleAsMammal is a convenience function that returns Whale wrapped in Mammal
+func WhaleAsMammal(v *Whale) Mammal {
+    return Mammal{ Whale: v}
+}
+
+// ZebraAsMammal is a convenience function that returns Zebra wrapped in Mammal
+func ZebraAsMammal(v *Zebra) Mammal {
+    return Mammal{ Zebra: v}
+}
+
+
 // Unmarshl JSON data into one of the pointers in the struct
 func (dst *Mammal) UnmarshalJSON(data []byte) error {
 	var err error