Typescript nullable Array

Question

I am testing Typescript and I ran into troubles with Array, interface and nullable variable :

I have this interface :

interface Entity {
    life: number;
    type: EntityType;
}

And I have this property :

world: Entity[];

I am trying to initialize with :

this.world = [
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null]
];

The compiler told me :

Cannot convert {}[] to Entity[]

Is this possible ? Am I doing something wrong.

Thanks in advance !

PS : Sorry for my english, I am not a native speaker.

Jeffery Grajkowski · Accepted Answer · 2014-02-18 16:19:42Z

4

What's happening here is TypeScript is inferring the type of the assignment, and because all the entries in the array are null it's inferring a type of {}[][]. {}[][] isn't assignable to Entity[][] so that's a compile error.

You can make the code compile with a ~~cast~~ type assertion. There's also an error in your code in that you've defined an array of arrays (2D) but world is declared as a 1D array. I assume you intend a 2D array there.

var world: Entity[][];

world = <Entity[][]>[
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null],
    [null, null, null, null, null, null, null, null]
];

edited Feb 18, 2014 at 16:19

answered Feb 17, 2014 at 17:16

Jeffery Grajkowski

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2 Comments

fharreau Over a year ago

Yeah, I understood why the compiler was angry. Thanks for the cast syntax. I didn't know it. Thanks for the 2D Array grammar too. I didn't know this grammar was possible in Typescript.

Fenton Over a year ago

+1. This is called a "type assertion" in TypeScript.

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