[Swift4] Model object cannot handle recursion

[Zexbe]

Description

Swagger-codegen fails to handle recursion after switching to structs.

Swagger-codegen version

2.4.0

Swagger declaration file content or url

swagger: "2.0"
info:
  title: "Example"
  version: "1.0.0"
host: "store.example.com"
basePath: "/v2"
schemes:
- "http"
paths:
  /category/{categoryId}:
    get:
      summary: "Find category by ID"
      operationId: "getCategoryById"
      produces:
      - "application/json"
      parameters:
      - name: "categoryId"
        in: "path"
        description: "ID of category to return"
        required: true
        type: "integer"
        format: "int64"
      responses:
        200:
          description: "successful operation"
          schema:
            $ref: "#/definitions/Category"
        400:
          description: "Invalid ID supplied"
        404:
          description: "Category not found"
definitions:
  Category:
    type: "object"
    properties:
      id:
        type: "integer"
        format: "int64"
      name:
        type: "string"
      parent:
        $ref: "#/definitions/Category"
      children:
        type: array
        items:
          $ref: "#/definitions/Category"
    xml:
      name: "Category"

Command line used for generation

-l swift4

Steps to reproduce

Generate client with swagger provided.
Add client to xcode project
Try to compile.

Related issues/PRs

#4126

Suggest a fix/enhancement

• https://stackoverflow.com/questions/36080491/swift-struct-type-recursion
• Fall back to classes in some situations
• Add option to use classes instead of struct (or just use class by default)

[goors]

Same here