{"record":{"id":"d396e42df3f48155","repo":"lysine-dev/retrofit","slug":"result-must-be-parameterized-as-result-foo-or-res-d396e4","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/rxjava2/src/main/java/retrofit2/adapter/rxjava2/RxJava2CallAdapterFactory.java","lineNumber":138,"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 RxJava2CallAdapter(\n        responseType, scheduler, isAsync, isResult, isBody, isFlowable, isSingle, isMaybe, false);\n  }\n}\n","sourceCodeStart":120,"sourceCodeEnd":152,"githubUrl":"https://github.com/lysine-dev/retrofit/blob/d0b112dad073b7fe49c953ebc46ff1b424cb1e51/retrofit-adapters/rxjava2/src/main/java/retrofit2/adapter/rxjava2/RxJava2CallAdapterFactory.java#L120-L152","documentation":"The RxJava 2.x adapter's Result<T> wrapper delivers either a Response or a network error as in-stream data (rather than via onError). A raw Result (e.g. Observable<Result>) provides no body type to deserialize, so RxJava2CallAdapterFactory 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 and 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 error-in-stream semantics are not required."],"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 assertRx2ResultParameterized(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.rxjava2.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 generic, not a marker."],"tags":["retrofit","rxjava2","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"}