{"id":1454,"date":"2014-09-23T10:43:31","date_gmt":"2014-09-23T01:43:31","guid":{"rendered":"http:\/\/kazu.tv\/blog\/?p=1454"},"modified":"2014-09-23T10:45:13","modified_gmt":"2014-09-23T01:45:13","slug":"scala-type-parameters","status":"publish","type":"post","link":"https:\/\/kazu.tv\/blog\/2014\/09\/23\/scala-type-parameters\/","title":{"rendered":"Scala\u306e\u578b\u5f15\u6570\u3068\u304b\u30b5\u30d6\u578b\u3068\u304b"},"content":{"rendered":"

\u30b3\u30f3\u30d1\u30a4\u30eb\u304c\u901a\u3089\u306a\u3044<\/h2>\n

\u4ee5\u4e0b\u306e\u30b3\u30fc\u30c9\u306e\u30b3\u30f3\u30d1\u30a4\u30eb\u304c\u901a\u3089\u306a\u3044\u306e\u3067\u3001\u3069\u3046\u3057\u305f\u3082\u306e\u304b\u3068\u8cea\u554f<\/a>\u3057\u305f\u3002<\/p>\n

abstract class C\r\ncase class C1() extends C\r\ncase class C2() extends C\r\n\r\ntrait Service[T <: C] {\r\n  def getFoo(): Option[T]\r\n}\r\n\r\nobject Service {\r\n  \/\/ found   : List[Option[Any]]\r\n  \/\/ required: List[Option[T]]\r\n  def getAllFoos(services: List[Service[_]]): List[Option[C]] = {\r\n    services.map(_.getFoo())\r\n  }\r\n}\r\n<\/pre>\n
\uff08\u7b54\u3048\u3060\u3051\u77e5\u308a\u305f\u3044\u5834\u5408\u306f\u3001@gakuzzzz \u3055\u3093\u306e\u30b3\u30e1\u30f3\u30c8<\/a>\u304c\u7c21\u6f54\u304b\u3064\u5b8c\u5168\u306a\u5185\u5bb9\u306a\u306e\u3067\u305d\u3061\u3089\u3092\u53c2\u7167\u3002\uff09<\/p>\n
\u30a8\u30e9\u30fc\u306e\u539f\u56e0<\/h2>\n
\u3055\u3066\u3001\u30a8\u30e9\u30fc\u306e\u539f\u56e0\u306f @gakuzzzz \u3055\u3093\u306e\u89e3\u8aac\u306b\u3042\u308b\u901a\u308a\u3002<\/p>\n
\u30dd\u30a4\u30f3\u30c8\u306f trait Service[T <: C] \u306b\u3057\u305f\u5834\u5408\u3001 Service[C] \u3068 Service[C1] \u3068 Service[C2] \u304c\u5168\u7136\u95a2\u4fc2\u306a\u3044\u578b\u306b\u306a\u3063\u3066\u3057\u307e\u3046\u306e\u3067\u3001\u7d71\u4e00\u7684\u306b\u6271\u3048\u306a\u3044\u3063\u3066\u6240\u3067\u3059\u306d\u3002<\/p><\/blockquote>\n
\uff08\u306a\u305c\u5168\u7136\u95a2\u4fc2\u306a\u3044\u578b\u306b\u306a\u3063\u3066\u3057\u307e\u3046\u306e\u3060\u308d\u3046\u3002\u8abf\u3079\u306a\u3044\u3068\u3002\uff09<\/p>\n
\u8a66\u884c\u932f\u8aa4<\/h2>\n
@xuwei-k \u3055\u3093\u306b\u6559\u3048\u3066\u3082\u3089\u3063\u305f\u65b9\u6cd5<\/h3>\n
@xuwei-k \u3055\u3093\u306b\u6559\u3048\u3066\u3082\u3089\u3063\u305f\u65b9\u6cd5\u3060\u3068\u30b3\u30f3\u30d1\u30a4\u30eb\u306f\u901a\u3063\u305f\u3002<\/p>\n
object Service {\r\n  def getAllFoos[A <: C](services: List[Service[A]]): List[Option[C]] = {\r\n    services.map(_.getFoo())\r\n  }\r\n}\r\n<\/pre>\n
\u305f\u3060\u3001\u5143\u306egist\u3067\u7aef\u6298\u3063\u3066\u3057\u307e\u3063\u305f\u3093\u3060\u3051\u3069\u3001@gakuzzzz \u3055\u3093\u304c\u66f8\u3044\u305f\u3088\u3046\u306b\u3001\u5b9f\u969b\u306b\u306fService\u306f\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u7d99\u627f\u3057\u3066\u4f7f\u3046\u3053\u3068\u3092\u524d\u63d0\u3068\u3057\u3066\u308b\u3002<\/p>\n
object C1Service extends Service[C1] { def getFoo(): Option[C1] = None }\r\nobject C2Service extends Service[C2] { def getFoo(): Option[C2] = None }<\/pre>\n
services\u306bC1Service\u3068C2Service\u304c\u6df7\u3056\u3063\u305f\u3082\u306e\u3092\u6e21\u3059\u3068\u30a8\u30e9\u30fc\u306b\u306a\u3063\u305f\u3002<\/p>\n
scala> Service.getAllFoos(List(C1Service))\r\nres4: List[Option[C]] = List(None)\r\n\r\nscala> Service.getAllFoos(List(C2Service))\r\nres5: List[Option[C]] = List(None)\r\n\r\nscala> Service.getAllFoos(List(C1Service, C2Service))\r\n<console>:17: error: no type parameters for method getAllFoos: (services: List[Service[A]])List[Option[C]] exist so that it can be applied to arguments (List[Service[_ >: C2 with C1 <: Product with Serializable with C]])\r\n --- because ---\r\nargument expression's type is not compatible with formal parameter type;\r\n found   : List[Service[_ >: C2 with C1 <: Product with Serializable with C]]\r\n required: List[Service[?A]]\r\n              Service.getAllFoos(List(C1Service, C2Service))\r\n                      ^\r\n<console>:17: error: type mismatch;\r\n found   : List[Service[_ >: C2 with C1 <: Product with Serializable with C]]\r\n required: List[Service[A]]\r\n              Service.getAllFoos(List(C1Service, C2Service))\r\n<\/pre>\n
\u30a8\u30e9\u30fc\u306e\u610f\u5473\u304c\u3088\u304f\u5206\u304b\u3089\u306a\u3044\u304c\u3001\u300cService[C] \u3068 Service[C1] \u3068 Service[C2] \u304c\u5168\u7136\u95a2\u4fc2\u306a\u3044\u578b\u306b\u306a\u3063\u3066\u3057\u307e\u300d\u3063\u3066\u308b\u3068\u3044\u3046\u4e8b\u306a\u306e\u304b\u306a\u3002<\/p>\n
@gakuzzzz\u3055\u3093\u306b\u66f8\u3044\u3066\u3082\u3089\u3063\u305f\u65b9\u6cd51<\/h3>\n
\u3053\u3061\u3089<\/a>\u3002<\/p>\n
abstract class C\r\ncase class C1() extends C\r\ncase class C2() extends C\r\n\r\ntrait Service[+T <: C] { \/\/ \u3053\u3053\u304c\u30dd\u30a4\u30f3\u30c8\r\n  def getFoo(): Option[T]\r\n}\r\n\r\nobject Service {\r\n  def getAllFoos(services: List[Service[C]]): List[Option[C]] = {\r\n    services.map(_.getFoo())\r\n  }\r\n}\r\n\r\nobject C1Service extends Service[C1] { def getFoo(): Option[C1] = None }\r\nobject C2Service extends Service[C2] { def getFoo(): Option[C2] = None }\r\n\r\nService.getAllFoos(List(C1Service, C2Service))\r\n<\/pre>\n
\u3046\u307e\u304f\u884c\u3063\u305f\u3002<\/p>\n
\u3053\u308c\u3092 trait Service[+T <: C]<\/code> \u3068\u3059\u308c\u3070\u3001Service[C1]<\/code> \u3068 Service[C2]<\/code> \u304c Service[C]<\/code> \u306e\u30b5\u30d6\u578b\u3068\u898b\u505a\u305b\u308b\u3088\u3046\u306b\u306a\u308b\u306e\u3067 Service[C]<\/code> \u3068\u3057\u3066\u7d71\u4e00\u7684\u306b\u6271\u3048\u308b\u3088\u3046\u306b\u306a\u308a\u307e\u3059\u3002<\/p><\/blockquote>\n
\u3068\u306e\u3053\u3068\u3002<\/p>\n
@gakuzzzz\u3055\u3093\u306b\u66f8\u3044\u3066\u3082\u3089\u3063\u305f\u65b9\u6cd52<\/h3>\n
gist\u306f\u3053\u3061\u3089<\/a>\u3002<\/p>\n
abstract class C\r\ncase class C1() extends C\r\ncase class C2() extends C\r\n\r\ntrait Service {\r\n  type T <: C\r\n  def getFoo(): Option[T]\r\n}\r\n\r\nobject Service {\r\n  def getAllFoos(services: List[Service]): List[Option[C]] = {\r\n    services.map(_.getFoo())\r\n  }\r\n}\r\n\r\nobject C1Service extends Service { type T = C1; def getFoo(): Option[C1] = None }\r\nobject C2Service extends Service { type T = C2; def getFoo(): Option[C2] = None }\r\n\r\nService.getAllFoos(List(C1Service, C2Service))\r\n<\/pre>\n
\u3053\u3061\u3089\u306b\u95a2\u3057\u3066\u3082\u5148\u751f\u306e\u30b3\u30e1\u30f3\u30c8\u3002<\/p>\n
\u578b\u5f15\u6570\u3092\u6b62\u3081\u3066\u3001\u62bd\u8c61\u30e1\u30f3\u30d0\u578b\u3067\u3084\u308c\u3070\u3001Service<\/code> \u3068\u3044\u3046\u578b\u306f\u4e00\u3064\u306b\u306a\u308b\u306e\u3067\u3001\u3053\u3061\u3089\u3082 Service<\/code> \u3067\u7d71\u4e00\u7684\u306b\u6271\u3048\u308b\u3088\u3046\u306b\u306a\u308a\u307e\u3059\u3002 type T = C1<\/code> \u304c\u5fc5\u8981\u306a\u306e\u306f\u3053\u306e\u5834\u5408\u3067\u3059\u306d\u3002<\/p><\/blockquote>\n
\u4f7f\u3044\u5206\u3051<\/h2>\n
\u3053\u308c\u3082\u5148\u751f\u306e\u30b3\u30e1\u30f3\u30c8\u305d\u306e\u307e\u307e\u66f8\u3044\u3068\u304f\u3002<\/p>\n
\u5171\u5909\u3092\u4f7f\u3046\u304b\u3001\u62bd\u8c61\u30e1\u30f3\u30d0\u578b\u3092\u4f7f\u3046\u304b\u3001\u306e\u5224\u65ad\u57fa\u6e96\u3068\u3057\u3066\u306f\u3001\u300cC1\u306b\u7279\u5316\u3057\u305fService\u306e\u578b\u3092\u6271\u3044\u305f\u3044\u304b\u3069\u3046\u304b\u300d\u306b\u306a\u308b\u304b\u3068\u601d\u3044\u307e\u3059\u3002<\/p><\/blockquote>\n
\u306a\u308b\u307b\u3069\u3002<\/p>\n
\u8003\u3048\u305f\u3053\u3068<\/h2>\n
\u3053\u308c\u3060\u3051\u3060\u3068\u3001@xuwei-k \u3055\u3093\u3068 @gakuzzzz \u3055\u3093\u306e\u30b3\u30e1\u30f3\u30c8\u3092\u5207\u308a\u8cbc\u308a\u3057\u305f\u3060\u3051\u306a\u306e\u3067\u3001\u3082\u3046\u5c11\u3057\u66f8\u3044\u3066\u304a\u304f\u3002<\/p>\n
\u305d\u3082\u305d\u3082\u306e\u52d5\u6a5f<\/h3>\n
\u5b9f\u969b\u306e\u30b3\u30fc\u30c9\u3060\u3068\u3001C1\u3068\u304bC2\u306f\u30e6\u30fc\u30b6\u30fc\u306e\u5916\u90e8\u30a2\u30ab\u30a6\u30f3\u30c8\u3068\u306e\u9023\u643a\u60c5\u5831\u3067\u3001\u4f8b\u3048\u3070\u4ee5\u4e0b\u306e\u69d8\u306a\u3082\u306e\uff08\u7c21\u7565\u5316\u3057\u3066\u308b\u3051\u3069\uff09\u3002\u3069\u308c\u3068\u3082\u9023\u643a\u3057\u3066\u3044\u306a\u3044\u4eba\u3082\u3044\u308c\u3070\u3001\u5168\u3066\u3068\u9023\u643a\u3057\u3066\u3044\u308b\u4eba\u3082\u3044\u308b\u3002<\/p>\n
    \n
  • Facebook\u9023\u643a\u306e\u60c5\u5831: UserFacebookInfo<\/li>\n
  • Twitter\u9023\u643a\u306e\u60c5\u5831: UserTwitterInfo<\/li>\n
  • GitHub\u9023\u643a\u306e\u60c5\u5831: UserGitHubInfo<\/li>\n<\/ul>\n
    \u305d\u308c\u305e\u308c\u304c\u62bd\u8c61\u30af\u30e9\u30b9UserExternalAccountInfo\u3092\u7d99\u627f\u3057\u3066\u3044\u308b\u3002<\/p>\n
    \u3067\u3001Service\u306b\u5f53\u305f\u308b\u306e\u306f\u3044\u304f\u3064\u304b\u3042\u308b\u3051\u3069\u3001\u4f8b\u3048\u3070DAO\u3067\u3001\u305d\u308c\u305e\u308c\u9055\u3046\u30c6\u30fc\u30d6\u30eb\u306b\u30c7\u30fc\u30bf\u304c\u5165\u3063\u3066\u3044\u308b\u306e\u3067\uff08\u305d\u308c\u305e\u308c user_facebook_info, user_twitter_info, user_github_info \u30c6\u30fc\u30d6\u30eb\uff09\u3001\u5225\u3005\u306eDAO\u3092\u7528\u610f\u3057\u305f\u3002\u4ee5\u4e0b\u306e\u611f\u3058\u3002<\/p>\n
    trait ExternalAccountInfoDao[T <: UserExternalAccountInfo] {\r\n  def getInfo(userId: Int): Option[T]\r\n}\r\n\r\nobject ExternalAccountInfoDao {\r\n  def getAllAccounts(userId: Int): List[Option[UserExternalAccountInfo]] = {\r\n    val daos = List(UserFacebookInfoDao, UserTwitterInfoDao, UserGithubInfoDao)\r\n    daos.map(_.getInfo(userId))\r\n  }\r\n}\r\n\r\nobject UserFacebookInfoDao\r\n extends ExternalAccountInfoDao[UserFacebookInfo] {\r\n  def getInfo(userId: Int): Option[UserFacebookInfo] = { \/* code *\/ }\r\n}\r\n\/\/ UserTwitterInfoDao, UserGithubInfoDao \u3082\u540c\u69d8<\/pre>\n
    \uff08\u591a\u5206\u3082\u3063\u3068\u826f\u3044\u8a2d\u8a08\u304c\u3042\u308a\u305d\u3046\u306a\u306e\u3067\u3001\u30b3\u30e1\u30f3\u30c8\u5927\u6b53\u8fce\u3067\u3059\u3002\uff09<\/p>\n
    \u305d\u306e\u4ed6<\/h3>\n
    \u30b3\u30e1\u30f3\u30c8\u3067\u66f8\u3044\u3066\u3082\u3089\u3063\u305f\u30b3\u30fc\u30c9\u3092\u898b\u308c\u3070\u5185\u5bb9\u306f\u5206\u304b\u308b\u3093\u3060\u3051\u3069\u3001\u81ea\u5206\u3067\u3042\u3046\u3044\u3046\u30b3\u30fc\u30c9\u304c\u30d1\u30c3\u3068\u51fa\u3066\u3053\u306a\u3044\u3068\u3053\u308d\u304c\u5b9f\u529b\u4e0d\u8db3\u3060\u3068\u601d\u3063\u305f\u3002<\/p>\n
    \u4eba\u306e\u30b3\u30fc\u30c9\u3092\u6ca2\u5c71\u8aad\u3093\u3060\u308a\u3001\u5b9a\u77f3\uff08\u3044\u308f\u3086\u308b\u30c7\u30b6\u30a4\u30f3\u30d1\u30bf\u30fc\u30f3\uff09\u3092\u3082\u3063\u3068\u52c9\u5f37\u3057\u306a\u3044\u3068\u3044\u3051\u306a\u3044\u306a\u3068\u601d\u3063\u305f\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
    \u30b3\u30f3\u30d1\u30a4\u30eb\u304c\u901a\u3089\u306a\u3044 \u4ee5\u4e0b\u306e\u30b3\u30fc\u30c9\u306e\u30b3\u30f3\u30d1\u30a4\u30eb\u304c\u901a\u3089\u306a\u3044\u306e\u3067\u3001\u3069\u3046\u3057\u305f\u3082\u306e\u304b\u3068\u8cea\u554f\u3057\u305f\u3002 abstract class C case class C1() extends C case class C2() extend…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[20],"tags":[],"class_list":["post-1454","post","type-post","status-publish","format-standard","hentry","category-scala"],"_links":{"self":[{"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/posts\/1454","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/comments?post=1454"}],"version-history":[{"count":5,"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/posts\/1454\/revisions"}],"predecessor-version":[{"id":1459,"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/posts\/1454\/revisions\/1459"}],"wp:attachment":[{"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/media?parent=1454"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/categories?post=1454"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kazu.tv\/blog\/wp-json\/wp\/v2\/tags?post=1454"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}