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Function return-type with decomposition not inferred correctly #2968
Description
interface IAddressBook {}
interface INavModel {}
function foo() {
let a: IAddressBook = {};
let b: INavModel[] = [];
return [a, b];
}
let [p, q] = foo();
let x: IAddressBook = p;
let y: INavModel[] = q; // <- errortsc (1.5.0-alpha) complains:
destruction.ts(13,5): error TS2322: Type 'IAddressBook' is not assignable to type 'INavModel[]'.
Property 'length' is missing in type 'IAddressBook'.atom-typescript shows that foo has signature foo(): IAddressBook[] and both p and q have type IAddressBook
The error is solved when specifying the return type of foo explicitly like:
function foo(): [IAddressBook, INavModel[]] {...}Is this a known/explainable issue?
Activity
[-]Decomposition seems to mix-up function return type[/-][+]Function return-type with decomposition not inferred correctly[/+]RyanCavanaugh commentedon Apr 30, 2015
We don't infer tuple types from array literals.
If you write code like this:
We could either infer
x's type as[Cat, Dog, Animal], orAnimal[]. If we do the former, the next line of code is an error; if we do the latter, it's not.It's arguable in the abstract which behavior is preferable (you can make convincing examples either way just by changing the names of the variables), but we shipped the
Animal[]behavior and didn't want to have a breaking change.