type (
	MergeFunction func(dst, src protoreflect.Message)
	mergeOptions  struct {
		customMergeFn map[protoreflect.FullName]MergeFunction
	}
)
type OptionFn func(options mergeOptions) mergeOptions

func MergeFunctionOptionFn(name protoreflect.FullName, function MergeFunction) OptionFn {
	return func(options mergeOptions) mergeOptions {
		options.customMergeFn[name] = function
		return options
	}
}