Repository navigation
Bug report about keyof with class implements. #17822
Description
TypeScript Version: 2.4.2
Code
/*!
*
* Copyright 2017 - acrazing
*
* @author acrazing joking.young@gmail.com
* @since 2017-08-16 15:56:19
* @version 1.0.0
* @desc index.ts
*/
export interface IOptions {
name: string;
}
export function config<T extends IOptions, K extends keyof T>(key: K, value: T[K]): void {
console.log(key, value)
}
export interface IClass {
config<T extends IOptions, K extends keyof T>(key: K, value: T[K]): void;
}
export class Class implements IClass {
config<T extends IOptions, K extends keyof T>(key: K, value: T[K]): void {
console.log(key, value)
}
}Expected behavior:
No Error
Actual behavior:
index.ts(23,14): error TS2420: Class 'Class' incorrectly implements interface 'IClass'.
Types of property 'config' are incompatible.
Type '<T extends IOptions, K extends keyof T>(key: K, value: T[K]) => void' is not assignable to type '<T extends IOptions, K extends keyof T>(key: K, value: T[K]) => void'. Two different types with this name exist, but they are unrelated.
Types of parameters 'key' and 'key' are incompatible.
Type 'K' is not assignable to type '"name"'.
Type 'keyof T' is not assignable to type '"name"'.
Activity
aluanhaddad commentedon Aug 16, 2017
This seems to work in 2.3.3 and error in nightly.
ahejlsberg commentedon Aug 18, 2017
This is working as intended and is an effect of #16368. When relating the
configmethods in the example it isn't possible for the checker to conclude that theTtype parameters are related because no parameters useTin a manner from which inferences can be made. This also means that in calls toconfigit isn't possible to infer type arguments forT, so such calls will always just default to theIOptionsbound unless type arguments are explicitly specified--which in turn means theTtype argument is pretty much pointless.I suggest changing the declarations to:
mhegazy commentedon Sep 18, 2017
Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.