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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Generic inference inside of `pipe` is incorrect when strict mode is disabled","articleBody":"\u003c!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨\r\n\r\nHalf of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Even if you think you've found a *bug*, please read the FAQ first, especially the Common \"Bugs\" That Aren't Bugs section!\r\n\r\nPlease help us by doing the following steps before logging an issue:\r\n  * Search: https://github.com/Microsoft/TypeScript/search?type=Issues\r\n  * Read the FAQ: https://github.com/Microsoft/TypeScript/wiki/FAQ\r\n\r\nPlease fill in the *entire* template below.\r\n--\u003e\r\n\r\n\u003c!-- Please try to reproduce the issue with `typescript@next`. It may have already been fixed. --\u003e\r\n**TypeScript Version:**  2.9.2\r\n\r\n\u003c!-- Search terms you tried before logging this (so others can find this issue more easily) --\u003e\r\n**Search Terms:**\r\n\r\n**Code**\r\n\r\nWith strict mode disabled:\r\n\r\n```ts\r\ndeclare function pipe\u003cV0, T1, T2, T3\u003e(\r\n    fn0: (x: V0) =\u003e T1,\r\n    fn1: (x: T1) =\u003e T2,\r\n    fn2: (x: T2) =\u003e T3,\r\n): (x: V0) =\u003e T3;\r\n\r\ntype Option\u003cT\u003e = { t: T }\r\ndeclare function optionOf\u003cT\u003e(value: T | null | undefined): Option\u003cT\u003e\r\n\r\ndeclare function get(name: \"set-cookie\"): string[] | undefined;\r\ndeclare function get(name: string): string | undefined;\r\n\r\n// $ExpectType (x: {}) =\u003e Option\u003cstring\u003e\r\n// but got (x: {}) =\u003e Option\u003c{}\u003e\r\n// Note: with strict mode enabled, we get the expected type.\r\nconst fn = pipe(\r\n    ({}: {}) =\u003e 'foo',\r\n    string =\u003e get(string),\r\n    // Workaround: pass the function directly, instead of wrapping:\r\n    // get,\r\n    optionOf,\r\n);\r\n```\r\n\r\n**Related Issues:** \u003c!-- Did you find other bugs that looked similar? --\u003e\r\nThis is similar to—but not exactly the same as—other issues I've filed when trying to use `pipe`:\r\n- https://github.com/Microsoft/TypeScript/issues/25637\r\n- https://github.com/Microsoft/TypeScript/issues/25791","author":{"url":"https://github.com/OliverJAsh","@type":"Person","name":"OliverJAsh"},"datePublished":"2018-07-20T12:51:30.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":8},"url":"https://github.com/25826/TypeScript/issues/25826"}