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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Inconsistent type inferring behavior","articleBody":"# Bug Report\r\n\r\nHi, we're having issues using inline call of the generic function decorator in a specific context. Unfortunately, I couldn't find anything related to this on stackoverflow, or here. Please check out the code below and feel free to let me know if more information/context is needed. Thanks!\r\n\r\n### 🔎 Search Terms\r\n\r\n* `infer generic`\r\n* `infer generic function`\r\n\r\n\u003c!--\r\n  What search terms did you use when trying to find an existing bug report?\r\n  List them here so people in the future can find this one more easily.\r\n--\u003e\r\n\r\n### 🕗 Version \u0026 Regression Information\r\n\r\n\u003c!-- When did you start seeing this bug occur?\r\n\r\n\"Bugs\" that have existed in TS for a long time are very likely to be FAQs; refer to\r\n  https://github.com/Microsoft/TypeScript/wiki/FAQ#common-bugs-that-arent-bugs\r\n\r\nIf possible, please try testing the nightly version of TS to see if it's already been fixed.\r\nFor npm: `typescript@next`\r\nThis is also the 'Nightly' version in the playground: http://www.typescriptlang.org/play/?ts=Nightly\r\n\r\nNote: The TypeScript Playground can be used to try older versions of TypeScript.\r\n\r\nPlease keep and fill in the line that best applies:\r\n--\u003e\r\nThis is the behavior in every version I tried, and I reviewed the FAQ for entries about **inference** and **generics**\r\n\r\n\r\n### ⏯ Playground Link\r\n\r\n\u003c!--\r\n  A link to a TypeScript Playground \"Share\" link which shows this behavior\r\n\r\n  The TypeScript Workbench can be used for more complex setups, try\r\n  https://www.typescriptlang.org/dev/bug-workbench/\r\n\r\n  As a last resort, you can link to a repo, but these will be slower for us to investigate.\r\n--\u003e\r\n[Playground link with relevant code](https://www.typescriptlang.org/play?ts=5.0.4#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-PzebwAPQA-L8M+QAsBYgBRcgQAAWtHSYG1PQ1PTglOdkM2HlpDbJiDD2NxgYyIbDEdl2Jj8Z0bqwuAI3q4vv4-v7j0numTxlMynTdjxuZzucQheLVjLlerdd7OpbbY7iEYXedQA)\r\n\r\n### 💻 Code\r\n\r\n\u003c!-- Please post the relevant code sample here as well--\u003e\r\n```ts\r\nfunction deferQuery\u003cTData\u003e({}: {\r\n  queryFn: () =\u003e Promise\u003cTData\u003e;\r\n  onSuccess: (data: TData) =\u003e void;\r\n}) {\r\n    // ...\r\n}\r\n\r\nexport function decorate\u003cTParams extends unknown[], TResult\u003e(\r\n  func: (...params: TParams) =\u003e Promise\u003cTResult\u003e,\r\n  ...params: TParams\r\n): () =\u003e Promise\u003cTResult\u003e {\r\n  return () =\u003e {\r\n    // ...\r\n    return func(...params);\r\n  };\r\n}\r\n\r\ntype ArbitraryData = {\r\n  property: string;\r\n};\r\n\r\nexport function getArbitraryData(_id: number): Promise\u003cArbitraryData[]\u003e {\r\n  return Promise.resolve([{property: '123'}]);\r\n}\r\n\r\ndeferQuery({\r\n  queryFn: decorate(getArbitraryData, 10),\r\n  onSuccess(data) {\r\n    //      ^? (parameter) data: unknown\r\n    data.forEach(console.log);\r\n  },\r\n});\r\n\r\nconst getData = decorate(getArbitraryData, 10);\r\ndeferQuery({\r\n  queryFn: getData,\r\n  onSuccess(data) {\r\n    //      ^? (parameter) data: ArbitraryData[]\r\n    data.forEach(console.log);\r\n  },\r\n});\r\n```\r\n\r\n### 🙁 Actual behavior\r\n\r\n`data` is typed as `ArbitraryData[]` only when the decorated method is stored in a variable.\r\n\r\n### 🙂 Expected behavior\r\n\r\n`data` is typed as `ArbitraryData[]` in both cases.\r\n\r\n```ts\r\ndeferQuery({\r\n  queryFn: decorate(getArbitraryData, 10),\r\n  onSuccess(data) {\r\n    //      ^? (parameter) data: ArbitraryData[]\r\n    data.forEach(console.log);\r\n  },\r\n});\r\n\r\nconst getData = decorate(getArbitraryData, 10);\r\ndeferQuery({\r\n  queryFn: getData,\r\n  onSuccess(data) {\r\n    //      ^? (parameter) data: ArbitraryData[]\r\n    data.forEach(console.log);\r\n  },\r\n});\r\n```\r\n","author":{"url":"https://github.com/chernodub","@type":"Person","name":"chernodub"},"datePublished":"2023-04-14T09:29:28.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/53776/TypeScript/issues/53776"}