Alias for TypeScript arrays

Question

I want to do a translation of C# code below into TypeScript:

[JsType(JsMode.Json)]
public class position : JsArray<JsNumber>
{
}

[JsType(JsMode.Json)]
public class coordinateArray : JsArray<position>
{
}

[JsType(JsMode.Json)]
public class polygonRings : JsArray<coordinateArray>
{
}

I tried to do it like this:

export interface position {
    (): number[];
}

export interface coordinateArray {
    (): position[];
}

export interface polygonRings {
    (): coordinateArray[];
}

But when I try to cast it I have some problems:

Cannot convert 'coordinateArray' to 'position[]'.

In code:

(<position[]> lineString.coordinates).push(position);

Ryan Cavanaugh · Accepted Answer · 2013-02-19 16:35:40Z

2

export interface coordinateArray {
    (): position[];
}

What you've described isn't an array, it's a function type that, when invoked, returns an array:

var x: coordinateArray = ...;
var y = x(); // y: position[]

You probably want to define an index signature instead:

export interface coordinateArray {
    [index: number]: position;
}

This won't convert directly to a position[] because it's still not actually an array (a real position[] would have methods like splice and push, but coordinateArray doesn't), but is at least correct about what the shape of the type is.

answered Feb 19, 2013 at 16:35

Ryan Cavanaugh

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Comments

Fenton · Accepted Answer · 2013-02-18 16:03:27Z

1

Calling the constructor method on an instance of coordinateArray would return type position[], but using the interface as a type wouldn't give you something compatible with position[].

If you have code that otherwise works, except for the compiler warning, you can tell the compiler you know better using:

(<position[]><any> ca)

answered Feb 18, 2013 at 16:03

Fenton

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