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Cannot use generics in JSDoc object signature #27215
Description
TypeScript does not appear to support using generics in JSDoc Object types (Object<string, T>). Doing so results in errors like Index signatures are incompatible. Type 'T' is not assignable to type 'string'..
TypeScript Version: 3.1.0-dev.20180919
Search Terms:
jsdoc object genericobject generic is not assignable to typejsdoc object generic index signature
Code
/**
* @param {T} val The value.
* @return {Object<string, T>} The object.
* @template T
*/
const createGenericObject = function(val) {
return {
'key': val
};
};
/**
* @const
* @type {Object<string, string>}
*/
const myStringObject = createGenericObject('hello');
/**
* @const
* @type {Object<string, number>}
*/
const myNumberObject = createGenericObject(42);Expected behavior:
No errors.
Actual behavior:
objectgeneric.js:16:7 - error TS2322: Type '{ [x: string]: T; }' is not assignable to type '{ [x: string]: string; }'.
Index signatures are incompatible.
Type 'T' is not assignable to type 'string'.
16 const myStringObject = createGenericObject('hello');
~~~~~~~~~~~~~~
objectgeneric.js:22:7 - error TS2322: Type '{ [x: string]: T; }' is not assignable to type '{ [x: string]: number; }'.
Index signatures are incompatible.
Type 'T' is not assignable to type 'number'.
22 const myNumberObject = createGenericObject(42);
~~~~~~~~~~~~~~
Playground Link: Not applicable (tsc behavior).
Related Issues: None found.
Activity
schmidtk commentedon Oct 9, 2018
Andy (Andrewkraft) (@Andy-MS) / Nathan Shively-Sanders (@sandersn): Is this something that could make the 3.2 milestone? I'm trying to get a rough estimate for planning purposes. Thanks for your time!
sandersn commentedon Oct 9, 2018
Kevin Schmidt (@schmidtk) It's planned for 3.2, and next on my list after improving the infer-from-usage codefix (#27610). It's not a simple fix — JSDoc generics do not create actual generic types right now — so plan like you would for any software engineering estimate.
schmidtk commentedon Oct 9, 2018
Nathan Shively-Sanders (@sandersn) Excellent, appreciate the feedback. Thank you!
sandersn commentedon Oct 12, 2018
Duplicate of #26883
Fearnbuster commentedon Nov 22, 2019
Does anyone have a guess as to why I'm still encountering these kind of errors?
I literally just copy and pasted the code from the original poster, and I'm getting errors that were identical to his.
I tried to install the latest version of Typescript (currently 3.7), but that didn't help anything.