{"record":{"id":"da51ea375b8d1ca1","repo":"lysine-dev/retrofit","slug":"result-must-be-parameterized-as-result-foo-or-res","errorCode":null,"errorMessage":"Result must be parameterized as Result<Foo> or Result<? extends Foo>","messagePattern":"Result must be parameterized as Result<Foo> or Result<\\? extends Foo>","errorType":"exception","errorClass":"IllegalStateException","httpStatus":null,"severity":"error","filePath":"retrofit-adapters/rxjava/src/main/java/retrofit2/adapter/rxjava/RxJavaCallAdapterFactory.java","lineNumber":134,"sourceCode":"              + \" return type must be parameterized\"\n              + \" as \"\n              + name\n              + \"<Foo> or \"\n              + name\n              + \"<? extends Foo>\");\n    }\n\n    Type observableType = getParameterUpperBound(0, (ParameterizedType) returnType);\n    Class<?> rawObservableType = getRawType(observableType);\n    if (rawObservableType == Response.class) {\n      if (!(observableType instanceof ParameterizedType)) {\n        throw new IllegalStateException(\n            \"Response must be parameterized\" + \" as Response<Foo> or Response<? extends Foo>\");\n      }\n      responseType = getParameterUpperBound(0, (ParameterizedType) observableType);\n    } else if (rawObservableType == Result.class) {\n      if (!(observableType instanceof ParameterizedType)) {\n        throw new IllegalStateException(\n            \"Result must be parameterized\" + \" as Result<Foo> or Result<? extends Foo>\");\n      }\n      responseType = getParameterUpperBound(0, (ParameterizedType) observableType);\n      isResult = true;\n    } else {\n      responseType = observableType;\n      isBody = true;\n    }\n\n    return new RxJavaCallAdapter(\n        responseType, scheduler, isAsync, isResult, isBody, isSingle, false);\n  }\n}\n","sourceCodeStart":116,"sourceCodeEnd":148,"githubUrl":"https://github.com/lysine-dev/retrofit/blob/d0b112dad073b7fe49c953ebc46ff1b424cb1e51/retrofit-adapters/rxjava/src/main/java/retrofit2/adapter/rxjava/RxJavaCallAdapterFactory.java#L116-L148","documentation":"The RxJava 1.x adapter's Result<T> wrapper packages either a Response or an error into the stream so that network failures are delivered as data rather than via onError. A raw Result (Observable<Result>) gives the adapter no body type to deserialize, so RxJavaCallAdapterFactory throws IllegalStateException when the inner observableType is Result.class but not a ParameterizedType.","triggerScenarios":"A method like `Observable<Result> getUser();` — Result used without its type argument. Thrown after `getRawType(observableType) == Result.class` when observableType is not a ParameterizedType.","commonSituations":"Using Result to swallow network errors in-stream but forgetting the body generic; copy-paste from samples.","solutions":["Parameterize Result: `Observable<Result<User>> getUser(@Path(\"id\") long id);`","Switch to Response or body-only if you do not need error-in-stream semantics."],"exampleFix":"// before\nObservable<Result> getUser(@Path(\"id\") long id);\n// after\nObservable<Result<User>> getUser(@Path(\"id\") long id);","handlingStrategy":"validation","validationCode":"import java.lang.reflect.*;\nstatic void assertRxResultParameterized(Class<?> iface) {\n  for (Method m : iface.getDeclaredMethods()) {\n    if (!(m.getGenericReturnType() instanceof ParameterizedType)) continue;\n    Type inner = ((ParameterizedType) m.getGenericReturnType()).getActualTypeArguments()[0];\n    if (inner.getTypeName().startsWith(\"retrofit2.adapter.rxjava.Result\") && !(inner instanceof ParameterizedType)) {\n      throw new AssertionError(\"Raw nested Result on \" + m);\n    }\n  }\n}","typeGuard":null,"tryCatchPattern":"try {\n  Observable<Result<User>> o = service.getUser(id);\n} catch (IllegalStateException e) {\n  throw new IllegalStateException(\"Nested Result return type is raw: \" + e.getMessage(), e);\n}","preventionTips":["Fail builds on raw types (-Xlint:rawtypes).","Unit-test that nested Result types are parameterized.","Remember Result is itself generic, not a marker class."],"tags":["retrofit","rxjava","generics","java","type-system","result"],"backgroundTag":null,"analyzedSha":"d0b112dad073b7fe49c953ebc46ff1b424cb1e51","analyzedAt":"2026-08-13T23:49:47.955Z","schemaVersion":2},"datasetVersion":"2026-08-14T00:17:13.853Z"}