[REQ] [Go] Mixed pointer/non-pointer usage leads to messy nested types

Is your feature request related to a problem? Please describe.

The Go code generator was updated in version 5.0 to support distinction between set/unset fields. While this may be a useful addition in some scenarios, there is a flaw in how Getters for nested types are represented: They act on a pointer, but return a plain object instead of a pointer. This makes it impossible to chain Get*() calls, because Go doesn't allow taking the address of a return value, neither implicitly nor explicitly.

Describe the solution you'd like

Ideally, the concept of "set" and "unset" should be dropped in favor of plain Go data structures, using pointers where a field is optional. When a default value is defined, it should be assigned during deserialization.

As a simpler alternative, getters on complex data types should return a pointer instead of a plain object.

Describe alternatives you've considered

The alternative would be to assign every nested field in a chain to a temporary variable, then call the next getter on this variable. This is awkward and not very idiomatic.

Additional context

Here's an example OpenAPI definition:

openapi: "3.0.1"
components:
  schemas:
    Container:
      type: "object"
      properties:
        nestedfield:
          $ref: "#/components/schemas/Child"
    Child:
      type: "object"
      properties:
        field:
          type: "boolean"

The generated Go code will look similar to this:

type Container struct {
	Nestedfield *Child
}
func (o *Container) GetNestedfield() Child {
	if o == nil || o.Nestedfield == nil {
		var ret Child
		return ret
	}
	return *o.Nestedfield
}
type Child struct {
	Field *bool
}
func (o *Child) GetField() bool {
	if o == nil || o.Field == nil {
		var ret bool
		return ret
	}
	return *o.Field
}

Testing it with a simple, straight-foward example like

func main() {
	var c *Container
	c.GetNestedfield().GetField()
}

Will yield:

./prog.go:24:20: cannot call pointer method on c.GetNestedfield()
./prog.go:24:20: cannot take the address of c.GetNestedfield()

Start by reproducing the issue with the OpenAPI Container and Child schemas and the generated Go types and main example shown here. Compare the nested getter signatures and verify the chosen pointer or set/unset behavior; done means nested Get* calls can be chained without the reported compilation errors while optional fields and defaults remain correct.